The foundational principle regarding blood in Islam is its prohibition for consumption, a command reiterated across several Quranic verses. Allah states unequivocally: 2:173, a prohibition repeated almost verbatim in 16:115. Surat Al-Ma'idah further confirms this, listing 2:173 among other forbidden things. These verses establish a clear divine decree that guides the dietary choices of Muslims.

The Quran, however, provides a crucial clarification regarding the type of blood that is prohibited. Surat Al-An'am specifies blood spilled out, indicating that it is the flowing blood, expelled during slaughter, that is impure and unlawful for consumption. Ibn Kathir explains that this refers to "flowing blood," a view echoed by Tafsir al-Jalalayn. Ma'arif-ul-Quran elaborates, noting that the word "dam" (blood) in its absolute sense is qualified by "massfuhan" (that which flows) in 6:145, leading to a consensus among jurists that congealed blood, such as liver and spleen, is clean and permissible. This distinction is further supported by a Hadith where the Prophet (ﷺ) stated, [We have been allowed two dead things and two bloody things: fish and locusts; and liver and spleen](Sahih Muslim 3:208, 5:3). This prophetic elaboration, as cited by Ibn Kathir, clarifies the scope of the Quranic prohibition, making it precise and practical for daily life.

The prohibition of flowing blood extends beyond mere consumption; it is also deemed impure (najis) for external use. Ma'arif-ul-Quran states that as eating or drinking blood is forbidden, so is its external use, buying, selling, and deriving any benefit from it, underscoring its complete unlawfulness due to its impurity.

The Sunnah of the Prophet Muhammad (ﷺ) provides further details and practical applications of the Quranic injunctions regarding blood. The Prophet's teachings emphasize the importance of ensuring blood drains from an animal during slaughter, an act known as dhabiha, to render the meat pure and lawful. Rafi` bin Khadij reported the Prophet's instruction, [If the killing tool causes blood to gush out, and if Allah's Name is mentioned, eat (of the slaughtered animal). But do not slaughter with a nail or a tooth, for the nail is the knife of Ethiopians and a tooth is a bone]Sahih al-Bukhari 72:29. This highlights that the method of slaughter must effectively remove the blood, and the tool used must be sharp enough to achieve this, while also mentioning Allah's name, signifying the intention of dedicating the act to Him.

The Prophetic Sunnah also clarified matters of ritual purity concerning blood. `Aisha reported that the Prophet (ﷺ) instructed a woman with menses to [give up the prayer when your menses begin and when it has finished, wash the blood off your body (take a bath) and start praying]Sahih al-Bukhari 6:35. This demonstrates that menstrual blood, being flowing blood, necessitates ritual purification (ghusl) and temporarily restricts certain acts of worship like prayer. For blood on garments, `Aisha narrated that the Prophet (ﷺ) advised women to [take hold of the blood spot and rub the blood off her garment, and pour water over it and wash that portion thoroughly and sprinkle water over the rest of the garment]Sahih al-Bukhari 6:13, indicating that simple washing is sufficient for removing blood stains from clothes for prayer.

An interesting exception in the Sunnah concerns martyrs. Jabir bin `Abdullah narrated that the Prophet (ﷺ) ordered the martyrs of Uhud to be [buried with blood on their bodies. Neither did he offer their funeral prayer nor did he get them washed]Sahih al-Bukhari 0:0. This special ruling for martyrs, whose blood is considered a mark of their sacrifice in Allah's cause, highlights a unique spiritual status. Abu Huraira further clarifies this, stating that [A wound which a Muslim receives in Allah's cause will appear on the Day of Resurrection as it was at the time of infliction; blood will be flowing from the wound and its color will be that of the blood but will smell like musk]Sahih al-Bukhari 4:103. This shows that the blood of a martyr is not deemed impure in the same way as other flowing blood; rather, it carries a symbolic purity and a distinct spiritual fragrance on the Day of Judgment.

Islamic scholars and jurists have extensively deliberated on the Quranic and Prophetic texts concerning blood, solidifying specific legal rulings. The explicit prohibition of "blood poured forth" (dam masfuh) in 6:145 is crucial for understanding the scope of what is forbidden. As Ma'arif-ul-Quran notes, this verse clarifies that it is specifically the flowing blood that is impure, allowing for the permissibility of organs like liver and spleen, which, despite being blood, are congealed and not considered "poured forth." Tafsir Ibn Kathir cites the Hadith regarding the permissibility of liver and spleen, reinforcing this interpretation.

The general prohibition of blood necessitates specific practices in animal slaughter. The Islamic method (dhabiha) requires the cutting of the jugular vein, windpipe, and esophagus to ensure the maximum drainage of blood, thereby rendering the meat lawful. The remaining blood within the meat and veins is not considered "poured forth" and is therefore permissible. This operationalization of the Quranic command is a cornerstone of halal meat production.

Furthermore, the jurists have discussed the issue of blood transfusion. Ma'arif-ul-Quran addresses this modern medical practice, acknowledging human blood as a part of the human body and impure (najis) when outside it. However, in situations of dire necessity where a patient faces a life-or-death situation and no other life-saving drug is effective or available, blood transfusion becomes permissible. This ruling draws an analogy with the Quranic exception for consuming forbidden foods under compulsion, likening blood to milk, which, though a bodily fluid, is permissible for consumption due to need. This reflects the Islamic principle of Allah is Forgiving and Merciful and the religion's emphasis on ease and preserving life.

Islam, while establishing clear prohibitions, is also a religion of ease and provides concessions in cases of extreme necessity. The Quranic verses explicitly state this: But whoever is forced [by necessity, neither desiring it nor transgressing its limit, there is no sin upon him. Indeed, Allah is Forgiving and Merciful]. This exception applies to all prohibited items, including blood, dead animals, and swine flesh. Surat Al-Ma'idah reinforces this, stating: 5:3.

Tafsir commentaries elaborate on the conditions for invoking this exception. Ma'arif-ul-Quran highlights two main conditions: first, the aim must be solely to save life, not to enjoy the forbidden food; second, one must eat only the minimum amount necessary to avert death, without transgressing the limit. Ibn Kathir clarifies that "without willful disobedience nor transgressing due limits" means not desiring the forbidden or overstepping the necessary amount. The act is not to be seen as making the forbidden lawful but rather as a forgiveness of the sin due to extreme compulsion. Masruq, as cited by Ibn Kathir, even implies that refusing to eat or drink until death in such a situation would lead to the Fire, underscoring the obligation to preserve life.

This principle extends to medical necessity. Ma'arif-ul-Quran outlines five conditions for using forbidden or impure substances as medicine: extreme necessity (life in danger), no lawful alternative being effective or available, certainty of cure, absence of enjoyment as an aim, and using no more than needed. This demonstrates the Shari'ah's flexibility and compassion in safeguarding human life and well-being, even when it involves momentarily setting aside general prohibitions.

Beyond the direct rulings on consumption, the prohibition of blood in Islam carries broader ethical and spiritual implications. The emphasis on purity and cleanliness (taharah) is central to Islamic practice, affecting diet, worship, and daily life. The meticulous nature of dhabiha, ensuring the drainage of blood, is not merely a hygienic practice but an act of obedience and reverence to divine command, distinguishing lawful from unlawful.

The Quranic verses about unlawful things are often juxtaposed with commands to eat from lawful and pure things (tayyibat) and to be grateful to Allah, the provider. Ibn Kathir explains that eating from pure sources is a cause for the acceptance of supplications and acts of worship, while eating from impure sources hinders them. This connection elevates dietary laws from mere legalistic rules to integral components of a believer's spiritual journey and their relationship with Allah. The Prophet's warning against consuming unlawful food hindering the acceptance of supplications (as cited by Ibn Kathir) reinforces this spiritual dimension.

The strict injunctions regarding blood, swine, and animals sacrificed to other than Allah serve to protect the monotheistic core of Islam, preventing practices that could dilute the singular worship of God. As Ma'arif-ul-Quran explains, slaughtering an animal for anyone other than Allah, even if Allah's name is recited, is forbidden because it embodies an intention of seeking favor from other entities, which is a form of Shirk (associating partners with Allah). This prohibition safeguards the purity of intention and action in worship, affirming that all blessings and acts of devotion are directed solely to Allah.

In essence, the Islamic stance on blood, meticulously detailed in the Quran and Sunnah and elaborated by scholars, forms a vital part of the comprehensive Islamic way of life. It balances strict adherence to divine commands with compassionate provisions for necessity, while always aiming to foster a deep sense of purity, obedience, and spiritual connection with the Divine.