The concept of sin is deeply rooted in the Quran, which provides both warnings against transgression and pathways to purification. Allah explicitly commands believers to leave what is apparent of sin and what is concealed thereof. Ibn Kathir explains that this verse encompasses all types of sins, public and secret, few or many. This comprehensive instruction emphasizes the importance of internal purity as much as external adherence to divine law. Qatadah expands on this, stating that this verse prohibits sins committed in public and secret alike. This reflects a holistic understanding of accountability, where even hidden intentions and thoughts are subject to divine scrutiny, as Allah states He is the All-Knower of what is in the breasts.

The Quran also warns against the consequences of denying divine guidance and persisting in sin. For instance, Woe to every sinful liar refers to those who deny Allah's signs and persist in their disbelief and arrogance. Tafsir al-Jalalayn clarifies that "woe" (waylun) implies chastisement for every sinful liar. Ibn Kathir elaborates that this refers to individuals who lie in speech, swear often, and deny Allah's verses, persisting in their disbelief as if they never heard them. Such individuals are promised a painful torment in the Hereafter. On the Day of Recompense, the disbelievers will admit their sin, so [it is alienation for the companions of the Blaze], highlighting a stark moment of self-admission and inevitable punishment. According to Ibn Kathir, this means they will have no recourse but to blame themselves.

Furthermore, the Quran highlights specific instances of sin. Prophet Musa (peace be upon him) acknowledged a “charge due to sin” against him when facing Pharaoh, referring to his accidental killing of an Egyptian man. Tafsir al-Jalalayn specifies this as "my slaying of the Egyptian man." This incident is an early example of a prophet recognizing a past error, even if unintentional, illustrating human fallibility.

The Sunnah, through the teachings of Prophet Muhammad (peace be upon him), further categorizes sins and provides practical guidance for their avoidance and expiation. The Prophet (peace be upon him) distinguished between minor and major sins. He frequently taught against "the seven great destructive sins," which include [to join others in worship along with Allah, to practice sorcery, to kill the life which Allah has forbidden except for a just cause, to eat up Riba (usury), to eat up an orphan's wealth, to give back to the enemy and fleeing from the battlefield at the time of fighting, and to accuse, chaste women, who never even think of anything touching chastity and are good believers]Sahih al-Bukhari 55:29Sahih al-Bukhari 86:79. Other hadith identify the "biggest of the great sins" as [to join others in worship with Allah, to be undutiful to one's parents, to kill a person, and to give a false witness]Sahih al-Bukhari 52:17Sahih Muslim 1:166. The emphasis on polytheism (Shirk) as the greatest sin is also echoed in the Quran, where it states that [Verily joining others in worship with Allah is a tremendous wrong indeed](6:82; 31:13, as explained by Ibn Kathir based on a hadith).

The Prophet also detailed the characteristics of a "sinful liar," referring to those who deny Allah's revelations and persist in their disbelief. This is reflected in the Quran's condemnation of every sinful liar. Such individuals, described by Ibn Kathir, are those who lie in speech, swear often, and commit sinful acts while disbelieving in Allah's signs. The Prophetic tradition offers a nuanced understanding of sin, recognizing that intentional acts of disobedience, especially those affecting others or denying the core tenets of faith, carry greater weight.

The Prophet's own supplications demonstrate a profound awareness of human susceptibility to sin. He sought refuge with Allah [from all sins, and from being in debt]Sahih al-Bukhari 43:13, explaining that a person in debt often lies and breaks promises, illustrating how one sin can lead to others. His prayers like, "O Allah! Set me apart from my sins (faults) as the East and West are set apart from each other and clean me from sins as a white garment is cleaned of dirt (after thorough washing). O Allah! Wash off my sins with water, snow and hail" Sahih al-Bukhari 10:138Sahih al-Bukhari 80:65Sahih al-Bukhari 80:72, highlight his constant striving for purification and teach believers the importance of humility and seeking divine cleansing.

Islamic teachings clearly outline the consequences of sin in both this world and the Hereafter, while also providing numerous avenues for expiation and forgiveness. The Quran states that those who earn [blame for sin will be recompensed for that which they used to commit], emphasizing divine justice. On the Day of Recompense, those whose scales are light will face Hawiyah, a name for Hellfire, as explained by Ibn Kathir as their ultimate abode. Conversely, those whose scales are heavy with good deeds will enjoy a pleasant life in Paradise. Ma'arif-ul-Quran further explains that the first weighing on the Day of Resurrection separates believers from non-believers, with belief (Iman) making scales heavy, while subsequent weighing distinguishes good from evil deeds among believers.

However, Allah's mercy is vast. Many hadith emphasize that various hardships and good deeds serve as expiations for sins. For instance, [no fatigue, nor disease, nor sorrow, nor sadness, nor hurt, nor distress befalls a Muslim, even if it were the prick he receives from a thorn, but that Allah expiates some of his sins for that]Sahih al-Bukhari 0:0Sahih al-Bukhari 75:2. Similarly, sincere illness is considered an expiation: [No Muslim is afflicted with any harm, but that his sins will be annulled as the leave of a tree fall down]Sahih al-Bukhari 75:21.

Specific acts of worship also offer forgiveness for past sins. The Prophet (peace be upon him) stated that [whoever establishes the prayers on the night of Qadr out of sincere faith and hoping to attain Allah's rewards (not to show off) then all his past sins will be forgiven]Sahih al-Bukhari 2:28. Similarly, fasting during Ramadan Sahih al-Bukhari 2:31Sahih al-Bukhari 30:11 and performing Hajj [without sexual relations with his wife, and does not do evil or sins then he will return (after Hajj free from all sins) as if he were born anew]Sahih al-Bukhari 25:9Sahih al-Bukhari 27:14 are powerful means of expiation. Even simple acts of remembrance, like saying "Subhan Allah wa bihamdihi" one hundred times a day, can lead to the forgiveness of sins, [even if they were as much as the foam of the sea]Sahih al-Bukhari 80:100.

The importance of seeking forgiveness is highlighted in the hadith where a servant repeatedly sins and repents, and Allah repeatedly forgives, saying, [My slave has known that he has a Lord who forgives sins and punishes for it, I therefore have forgiven my slave (his sins)]Sahih al-Bukhari 97:132. This emphasizes Allah's boundless mercy and His pleasure with those who turn to Him in repentance.

While all sins are acts of disobedience, some carry particular gravity, especially those that involve injustice towards others or open defiance of Allah. Causing harm to others, particularly believers, is highlighted as a serious offense. The Quran explicitly states, 33:58 other than what they have earned have certainly born upon themselves a slander and manifest sin]. Tafsir al-Jalalayn clarifies that this means accusing them of things they have not done. Ibn Kathir categorizes this as "the most serious slander," particularly condemning those who attribute shortcomings to the Companions undeservedly. Ma'arif-ul-Quran explains that causing pain to any Muslim without valid Shari'ah justification is haram, citing a hadith that a true Muslim is one from whose tongue and hands all Muslims remain unharmed.

A crucial distinction is made for public sins. The Prophet (peace be upon him) warned against the Mujahirin – those who commit sins openly or disclose their sins to others. He said, [All the sins of my followers will be forgiven except those of the Mujahirin... An example of such disclosure is that a person commits a sin at night and though Allah screens it from the public, then he comes in the morning, and says, 'O so-and-so, I did such-and-such (evil) deed yesterday,' though he spent his night screened by his Lord (none knowing about his sin) and in the morning he removes Allah's screen from himself]Sahih al-Bukhari 78:99. This hadith discourages not only open sin but also boasting about sins, as it removes Allah's screen and encourages others to view sin lightly.

Moreover, the concept of zulm (injustice or wrongdoing) is particularly emphasized when discussing Shirk (associating partners with Allah). The Quran states, It is those who believe and confuse not their belief with Zulm (wrong), for them (only) there is security and they are the guided. When the Companions of the Prophet initially found this verse difficult, fearing they all committed zulm against themselves, the Prophet clarified that zulm in this context specifically refers to Shirk, citing the verse Verily! Joining others in worship with Allah is a great Zulm (wrong) indeed (Sahih al-Bukhari 65:151, Ibn Kathir). Ma'arif-ul-Quran reinforces that zulm here is not sin in the ordinary sense but encompasses all kinds of Shirk, including taking saints or angels as partners in divine attributes.

Islamic teachings on sin emphasize a delicate balance between divine mercy and human responsibility. While Allah is 6:120 sin will be recompensed for that which they used to commit].

Despite the gravity of sin, Allah's mercy is always presented as overriding His wrath. A powerful Hadith Qudsi states, [My mercy overcomes My anger](Tafsir Ibn Kathir on 6:14). This divine attribute inspires hope and encourages repentance, as Allah [Stretches out His Hand during the night so that the people may repent for the fault committed from dawn till dusk and He stretches out His Hand during the day so that the people may repent for the fault committed from dusk to dawn]Sahih Muslim 0:0. This continuous invitation to repentance highlights that the door to forgiveness is always open until the final hour.

The narrative of Prophet Ibrahim (peace be upon him) in the Quran demonstrates reliance on divine forgiveness. When describing his hopes for the Day of Recompense, he stated, 26:82. Ibn Kathir explains that this refers to Allah being the only one capable of forgiving sins, highlighting the prophet's humility and trust in divine mercy.

The concept of "Allah's days" (أَيَّامَ اللَّهِ) in the Quran, referring to reward and punishment, serves as a reminder of ultimate accountability. While early Muslims were encouraged to forgive those who do not believe in Allah's days during a particular phase of Islam, this forgiveness did not negate the ultimate divine recompense. Ma'arif-ul-Quran explains this was a social law to avoid vengeance for every small thing, and that the ultimate "excruciating" punishment awaits disbelievers in the Hereafter. This interplay reveals that while Muslims are encouraged to show forbearance, divine justice will ultimately prevail.

Sins (ذُنُوب) in Islam are understood as a deviation from divine commands, with clear pronouncements in the Quran and elaborations in the Sunnah. From the command to avoid both apparent and concealed sins, to the identification of major transgressions like Shirk and false witness, Islamic texts delineate the spectrum of wrongful acts. Yet, woven throughout these warnings is an undeniable thread of divine mercy, emphasizing that repentance, sincere supplication, and righteous deeds are potent avenues for forgiveness. The Islamic framework of sin, therefore, is not one of despair but of constant striving, accountability, and hope in Allah's infinite compassion for those who sincerely turn to Him.