Musnad Abu Ya'la al-Mawsili 117:89

Abu al-Rabi' narrated to us, Hammad narrated to us, from Thabit, who said: Anas said to us: "I do not fall short in praying with you as I saw the Messenger of Allah (peace be upon him) praying with us." Thabit said: I saw Anas doing something that I do not see you doing. When he raised his head from the bowing (ruku'), he would stand until one saying would say, "He has forgotten." And when he raised his head from the first prostration (sujud), he would stand until one saying would say, "He has forgotten."