So prostrate to Allah and worship [Him]

The fa (so) is for sequencing the command or its implication based on what has been established regarding the invalidity of responding to the Qur’an with wonder and laughter, and the necessity of responding to it with what befits it and indicates the greatness of its status. That is: since the matter is such, prostrate to Allah the Exalted who revealed it, and worship Him, may His majesty be glorified.

This is a verse of prostration (sajdah) according to the majority of scholars, and the Prophet, may Allah bless him and grant him peace, prostrated upon reciting it.

The Two Shaykhs [Al-Bukhari and Muslim], Abu Dawud, An-Nasa’i, and Ibn Marduyah recorded from Ibn Mas‘ud that he said: "The first surah revealed containing a prostration was 'The Star' (An-Najm), so the Messenger of Allah, may Allah bless him and grant him peace, prostrated, and all the people prostrated except one man..." [the remainder of the tradition].

Ibn Marduyah and Al-Bayhaqi in Al-Sunan recorded from Ibn ‘Umar, may Allah be pleased with them both, that he said: "The Messenger of Allah, may Allah bless him and grant him peace, prayed with us, recited An-Najm, and prostrated with us, prolonging the prostration."

Likewise, ‘Umar, may Allah be pleased with him: Sa‘id ibn Mansur recorded from Sabrah that he said: "‘Umar ibn Al-Khattab led us in the Dawn prayer, and he recited Surah Yusuf in the first rak‘ah, then he recited Surah An-Najm in the second and prostrated; then he stood up and recited 'Itha Zulzilat', then he bowed."

Malik does not view prostration [as required] here, and he argued for this with what was recorded by Ahmad, the Two Shaykhs, Abu Dawud, At-Tirmidhi, An-Nasa’i, At-Tabarani, and others from Zayd ibn Thabit, who said: "I recited An-Najm before the Prophet, may Allah bless him and grant him peace, and he did not prostrate in it."

The response is that the omission [of the prostration] only contradicts the obligation of the prostration, and it is not a matter of consensus. According to those who hold it to be obligatory, such cases allow for deferment, according to the preferred opinion, and there is nothing in the hadith that indicates its absolute negation; thus, it is possible that he, peace and blessings be upon him, prostrated afterward, and likewise Zayd, may Allah be pleased with him. Indeed, delaying it is reprehensibly disliked (makruh tanzihan), and perhaps he did so to demonstrate permissibility or for an excuse of which we are not aware.

As for what Ibn Marduyah recorded from Ibn ‘Abbas, in his saying: "The Messenger of Allah, may Allah bless him and grant him peace, did not prostrate in any of the Mufassal [surahs] since he moved to Medina," it is a negation and it is weak. The same applies to his saying, in what was also narrated from him: "The Messenger of Allah, may Allah bless him and grant him peace, used to prostrate in An-Najm in Mecca, but when he migrated to Medina, he abandoned it," assuming that abandonment only contradicts, as you have heard, the obligation. And Allah the Exalted knows best.