Others held that it is sunnah rather than obligatory. This is the stronger view.

They cited the following evidence:

First: Zayd ibn Thabit, may Allah be pleased with him, recited Surat al-Najm to the Prophet, may Allah’s blessings and peace be upon him, and did not prostrate at its verse of prostration. (1) Had prostration been obligatory, the Prophet, may Allah’s blessings and peace be upon him, would not have approved of his omitting it.

If someone were to say: Is it not possible that Zayd was not in a state of ablution?

The answer is: This is possible, but it is not certain. Rather, the apparent assumption is that he was in a state of ablution, for it is unlikely that he would recite the Quran without ablution.

Moreover, had prostration been obligatory, the Prophet, may Allah’s blessings and peace be upon him, would have asked him for clarification: was he in a state of ablution, in which case he should prostrate, or was he without ablution, in which case he should not? This is just as the Prophet, may Allah’s blessings and peace be upon him, asked the man who entered the mosque while the Prophet was delivering the Friday sermon and then sat down. The Prophet, may Allah’s blessings and peace be upon him, said to him, “Have you prayed?” He replied, “No.” He said, “Then stand and pray two rak‘ahs.” (2)

Second: It is authentically reported from Umar ibn al-Khattab, may Allah be pleased with him, in Sahih al-Bukhari and elsewhere that he recited Surat al-Nahl from the pulpit. When he reached the verse of prostration, he descended from the pulpit and prostrated, and the people prostrated. Then, on the following Friday, he recited it but did not prostrate. He then said—so as to remove any doubt—“Allah has not made prostration obligatory upon us, unless we wish to do so.” (3) This was Umar’s statement—