Sayyiduna Anas (may Allah be pleased with him) narrates that when the Messenger of Allah (peace and blessings be upon him) would raise his head from bowing (ruku‘), we would remain standing until we saw him in the state of prostration (sajdah).
Hadith Referenceصحيح ابن خزيمه / جماع أبواب قيام المأمومين خلف الإمام وما فيه من السنن / 1598