Musannaf Ibn Abi Shayba 3:584

Shababa ibn Sawwar narrated to us, he said: Sulayman ibn al-Mughira narrated to us, he said: Thabit narrated to us, from Anas, who said: Anas described the prayer of the Prophet, may Allah bless him and grant him peace, to us. Then he stood to pray, so he bowed, then he raised his head from the bowing and stood upright until some of us thought that he had forgotten. He said: Then he prostrated, then he sat upright until some of us thought that he had forgotten.