Musannaf Ibn Abi Shayba 3:670

Ibn Numayr narrated to us, from al-‘Ala’ ibn Salih, from Salamah ibn Kuhayl, from Hujr ibn ‘Anbas, from Wa’il ibn Hujr, that he prayed behind the Prophet (may Allah bless him and grant him peace). When he recited the Opening of the Book (al-Fatihah), he said "Amin" aloud. He (Wa’il) said: And he (the Prophet) performed the taslim to his right and to his left, until I saw the whiteness of his cheek.