Narrated Mujahid:

I asked Ibn `Abbas, "Should we perform a prostration on reciting Surat-Sa`d?" He recited (the Sura) including: 'And among his progeny, David, Solomon..(up to)...so follow their guidance (6.84-91) And then he said, "Your Prophet is amongst those people who have been ordered to follow them (i.e. the preceding apostles).

Narrated Mujahid:

That he asked Ibn `Abbas, "Is there a prostration Surat-al-Sa`d?" (38.24) Ibn `Abbas said, "Yes," and then recited: "We gave...So follow their guidance." (6.85,90) Then he said, "He (David ) is one them (i.e. those prophets)." Mujahid narrated: I asked Ibn `Abbas (regarding the above Verse). He said, "Your Prophet (Muhammad) was one of those who were ordered to follow them."

Narrated Al-Awwam:

I asked Muhajid regarding the prostration in Surat Sa`d. He said, "Ibn `Abbas was asked the same question and he said, 'Those are they (the prophets) whom Allah had Guided. So follow their guidance." (6.90) Ibn `Abbas used to perform a prostration (on reading this Sura).

Narrated Al-Awwam:

I asked Mujahid regarding the prostration in Surat Sa`d. He said, "I asked Ibn `Abbas, 'What evidence makes you prostrate?' He said, "Don't you recite:--'And among his progeny, David and Solomon..(6.84). Those are they whom Allah had guided. So follow their guidance.' (6.90) So David was the one of those prophets whom Prophet (Muhammad) was ordered to follow. David prostrated, so Allah's Messenger (Muhammad) performed this prostration too.'