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
Sayyiduna Amr bin Huraith (may Allah be pleased with him) narrates that I prayed behind the Messenger of Allah (peace and blessings be upon him). When he would raise his head from bowing (ruku‘), none of us would bend our backs (for prostration) until we saw that the Messenger of Allah (peace and blessings be upon him) had completely gone into the state of prostration (sajdah).
Hadith Referenceصحيح ابن خزيمه / جماع أبواب قيام المأمومين خلف الإمام وما فيه من السنن / 1599