Musannaf Ibn Abi Shayba 3:1895

Mu'tamir ibn Sulayman narrated to us, from Abu Ma'n, from Abu al-'Aliyah, who said: Some of the companions of the Prophet (peace and blessings of Allah be upon him) used to prostrate during [the recitation of] Sad, and some of them would not prostrate. So, whichever of those you wish, do it.