Tafsir of Al-Inshiqaq 84:21

"And when the Quran is recited to them, they do not prostrate." This is a conjunctive clause to the preceding circumstantial (ḥāliyyah) clause, thus it is also circumstantial, like the one before it. That is: what prevents them from prostrating when the Quran is recited to them?

Prostration here is a metaphor for the submission that necessarily accompanies it, according to what has been narrated from Qatada; or, it is intended to mean the ritual prayer (ṣalāh). Linking this with belief is an indication of the greatness of its status, as is not hidden. Alternatively, it is to be taken literally, in which case what is intended by the preceding phrase is a specific recitation of the Quran, or a section containing a prostration verse (āyat sajdah).

It is authentically established from the Prophet—may Allah the Exalted grant him peace and blessings—that he prostrated when this verse was recited. Muslim, Abu Dawud, al-Tirmidhi, al-Nasa’i, Ibn Majah, and others reported from Abu Huraira that he said: "We prostrated with the Messenger of Allah—may Allah the Exalted grant him peace and blessings—during Idha al-sama'u inshaqqat (When the sky has split asunder) and Iqra' bismi rabbika (Read in the name of your Lord)."

The two Sheikhs (al-Bukhari and Muslim), Abu Dawud, and al-Nasa’i reported from Abu Rafi‘ that he said: "I prayed the evening prayer (‘atamah) with Abu Huraira, and he recited Idha al-sama'u inshaqqat, then he prostrated. I asked him about it, and he said: 'I prostrated behind Abu al-Qasim—may Allah the Exalted grant him peace and blessings—so I shall not cease to prostrate during it until I meet him—upon him be peace and blessings.'"

This constitutes a refutation of Ibn ‘Abbas—may Allah the Exalted be pleased with both of them—who said that there is no prostration in the Mufaṣṣal (the final section of the Quran). This surah is from the Mufaṣṣal according to the majority; some say it begins from Surah Muhammad, others say from Surah al-Fath, and others—which is the opinion of the majority—that it begins from Surah al-Hujurat.

The prostration is Sunnah according to al-Shafi‘i and Wājib (obligatory) according to Abu Hanifa. The Imam stated: It is narrated that one day the Prophet—may Allah the Exalted grant him peace and blessings—read "Prostrate and draw near" (wasjud wa-iqtarib), and he and those with him among the believers prostrated, while the Quraysh were clapping and whistling above their heads; then this verse was revealed.

Abu Hanifa argued for the obligation of this prostration from two aspects: First, the action of the Prophet—upon him be peace and blessings—necessitates obligation due to the words of the Exalted: "Follow him." Second, the Exalted dispraised those who hear it and do not prostrate; the occurrence of dispraise upon omission indicates obligation. The discussion concludes here. However, there is contention regarding this, as the hadith, as Ibn Hajar stated, is not established.