The Quran frequently addresses the faculty of speech, highlighting its power and the responsibility it entails. Believers are consistently urged to engage in virtuous communication, such as speaking to people good words and speaking words of appropriate uprightness. The gravity of speech is underscored by the divine declaration that not a word does one utter but there is by him an observer, ready to record, signifying ultimate accountability before Allah.

Beyond general ethical guidance, the Quran also directly addresses the Prophet Muhammad's use of his tongue during the reception of revelation. Multiple hadith from Bukhari and Muslim, narrated by Ibn Abbas and Said bin Jubair, explain the context of the verse Move not your tongue concerning (the Qur'an) to make haste therewith. These narrations describe the Prophet's initial struggle to instantly memorize the divine words as Gabriel delivered them, leading him to move his lips quickly out of eagerness. Allah, in His infinite wisdom, revealed this verse to reassure the Prophet that the preservation and recitation of the Quran were His responsibility. As Ibn Abbas explains, It is for Us to collect it (Qur'an) in your mind, and give you the ability to recite it by heart, meaning Allah would ensure its retention in the Prophet's chest and enable him to recite it. Furthermore, when We have recited it to you (O Muhammad through Gabriel) then follow you its recital meant to listen attentively and be silent. Finally, It is for Us to explain it and make it clear to you signifies that Allah would facilitate its explanation through the Prophet's tongue. This sequence illustrates the divine management of the most sacred form of speech – the Quran itself – and underscores the tongue's fundamental role as the vehicle for transmitting divine guidance to humanity.

The Sunnah provides extensive guidance on the proper use and control of the tongue, often presenting it as a direct path to Paradise or Hellfire. A foundational principle is articulated in the Prophet's saying, [Whoever can guarantee (the chastity of) what is between his two jaw-bones and what is between his two legs (i.e. his tongue and his private parts), I guarantee Paradise for him]Bukhari 81:63. This hadith, also reported by Sahl bin Sa'd Bukhari 86:36, elevates the control of the tongue and private parts to a condition for entering Paradise, highlighting their immense spiritual significance.

Another crucial prophetic teaching emphasizes the direct link between faith and speech. Abu Huraira reported the Prophet (peace be upon him) as saying, [Whoever believes in Allah and the Last Day should talk what is good or keep quiet]Bukhari 81:64. This profound statement establishes a direct correlation between one's belief in Allah and the Day of Judgment and the conscious control of one's speech, advocating for either beneficial speech or silent reflection. The emphasis on "what is good" suggests that speech should be constructive, truthful, and kind, aligning with the Quranic injunctions.

The Prophet's own character served as a powerful example. Anas reported that [Allah's Messenger (ﷺ) was neither a Fahish (one who had a bad tongue) nor a Sabbaba (one who abuses others)]Bukhari 78:76, demonstrating his impeccable conduct and restraint in speech even when admonishing others.

While highlighting the virtues of controlled speech, Islamic texts also powerfully warn against the destructive potential of an unrestrained tongue. The Prophet (peace be upon him) explicitly stated, [A Muslim is the one who avoids harming the Muslims with his tongue or his hands]Bukhari 81:73. This definition of a Muslim, reiterated by Abu Musa Bukhari 2:4 and Jabir Muslim 1:69, places safeguarding others from one's tongue on par with safeguarding them from physical harm, indicating the severe impact of verbal abuse and slander.

The dangers of careless speech are further elucidated by Abu Huraira, who narrated that [A slave of Allah may utter a word without thinking whether it is right or wrong, he may slip down in the Fire as far away a distance equal to that between the east]Bukhari 81:66. In another narration, he adds that [a slave (of Allah) may utter a word (carelessly) which displeases Allah without thinking of its gravity and because of that he will be thrown into the Hell-Fire]Bukhari 81:67. These hadith paint a stark picture of the consequences of heedless speech, emphasizing that even seemingly minor utterances can carry immense weight in the divine scale and lead to severe punishment.

Moreover, the tongue is identified as an instrument of "adultery" in a broader sense. Ibn Abbas and Abu Huraira reported the Prophet's teaching that [The adultery of the eye is the sight (to gaze at a forbidden thing), the adultery of the tongue is the talk, and the inner self wishes and desires and the private parts testify all this or deny it]Bukhari 79:17. Muslim's narration elaborates on this, stating that [the adultery of the tongue is the licentious speech]Muslim 46:32, reinforcing the idea that any form of forbidden or lustful communication falls under a category of moral transgression akin to physical adultery, demonstrating the profound spiritual impurity that can arise from uncontrolled speech.

Despite its dangers, the tongue is also presented as a powerful tool for worship and remembrance of Allah (dhikr). The Prophet (peace be upon him) highlighted the immense reward for uttering specific phrases of remembrance. Abu Huraira narrated that [There are two expressions which are very easy for the tongue to say, but they are very heavy in the balance and are very dear to The Beneficent (Allah), and they are, 'Subhan Allah Al-`Azim and 'Subhan Allah wa bihamdihi']Bukhari 80:101. This statement, echoed in other narrations Bukhari 97:188Muslim 48:41, encourages believers to engage their tongues in constant praise and glorification of Allah, showing that the same organ that can lead to sin can also be a source of immense spiritual merit and divine favor.

Furthermore, the tongue plays a crucial role in the recitation of the Quran. Umm Hisham bint Haritha b. Nu'man reported learning Surah Qaf directly [from the tongue of the Messenger of Allah (ﷺ) who used to recite it every Friday on the pulpit when he delivered the sermon to the people](Muslim 7:64, 7:65). This illustrates the Prophet's role in conveying the divine word through his speech, a practice that continues through generations of Quran reciters. However, the spiritual engagement with the Quran through the tongue is not merely mechanical. Jundub b. 'Abdullah al-Bajali reported the Prophet as saying, [Recite the Qur'an as long as your hearts agree to do so, and when you feel variance between them (between your hearts and tongues), then get up (and leave its recital for the time being)]Muslim 47:3. This hadith emphasizes the importance of internal spiritual harmony with the recitation, ensuring that the tongue's utterance is accompanied by a receptive heart. Similarly, for night prayers, Abu Huraira advised that if one's tongue falters in recitation and one does not know what is being recited, they [should go to sleep]Muslim 6:264, prioritizing focused and meaningful worship over mere lip service.

Interestingly, the Prophet's tongue is also presented as a conduit for divine will and mercy. Abu Musa narrated that whenever a beggar or needy person approached the Prophet, he would say to his companions, [Help and recommend him and you will receive the reward for it; and Allah will bring about what He will through His Prophet's tongue]Bukhari 24:35. This specific phrase, repeated in other narrations Bukhari 78:58Muslim 45:188, suggests a unique quality of the Prophet's speech, where his recommendations and pronouncements could align with and even initiate divine decrees, making his tongue a blessed instrument for the manifestation of Allah's will. This further elevates the significance of the tongue, particularly in the context of prophethood, as a channel for divine action and guidance.

In summary, the Islamic tradition views the tongue not merely as a physiological part but as a spiritual instrument of profound consequence. From its role in transmitting the divine revelation to its capacity for both immense good through dhikr and tremendous harm through backbiting and slander, the tongue is central to a Muslim's faith and practice. The consistent emphasis in the Quran and Sunnah on controlling, purifying, and utilizing one's speech for good underscores the belief that the proper management of "ما بين فكيه" is indeed a gateway to spiritual success and a hallmark of true piety.