I asked Muhajid regarding the prostration in Surat Sad. 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).
• Sahih al-Bukhari, Vol. 6, Book of Prophetic Commentary on the Qur'an, Hadith 330
• Sahih al-Bukhari, Book of Prophetic Commentary on the Qur'an, Hadith 330