It is narrated from Hazrat Saeed bin Jubair (may Allah have mercy on him) that Sayyiduna Ibn Abbas (may Allah be pleased with them both) used to perform sajdah in «‏‏‏‏سورۃ ص» ‏‏‏‏. So he was asked about this, and he recited this verse «‏‏‏‏أُولَٰئِكَ الَّذِينَ هَدَى اللَّهُ ۖ فَبِهُدَاهُمُ اقْتَدِهْ» ‏‏‏‏ [ سورة الأنعام ] "These are the ones whom Allah has guided." Therefore, follow their guidance. And he said that (on this verse) Hazrat Dawood (peace be upon him) performed sajdah and the Messenger of Allah (peace and blessings be upon him) also performed sajdah.

Hazrat Mujahid (may Allah have mercy on him) narrates that I asked Sayyiduna Ibn Abbas (may Allah be pleased with them both), "On what basis have you taken the prostration (sajdah) of Surah «‏‏‏‏ص» ‏‏‏‏?" He said that he recited this blessed verse to me: «‏‏‏‏وَمِن ذُرِّيَّتِهِ دَاوُودَ وَسُلَيْمَانَ وَأَيُّوبَ» ‏‏‏‏ (And among their descendants are Dawud, Sulaiman, and Ayyub) «‏‏‏‏أُولَٰئِكَ الَّذِينَ هَدَى اللَّهُ ۖ فَبِهُدَاهُمُ اقْتَدِهْ» ‏‏‏‏ (These are the ones whom Allah has guided, so follow their guidance). He said that Dawud (peace be upon him) performed sajdah in it, and that is why the Messenger of Allah (peace and blessings be upon him) also performed sajdah.