Musnad Ahmad 794:1

Muhammad ibn Abd al-Rahman al-Tafawi narrated to us, Sa'id al-Jurayri narrated to us, from a man from Banu Tamim—and he praised him well—from his father or his paternal uncle, who said: I prayed behind the Messenger of Allah, peace and blessings of Allah be upon him, and we asked him about the duration of his bowing and his prostration. He said: "The duration of what a man says: 'Subhan Allah wa bihamdihi' (Glory be to Allah and by His praise) three times."