Musnad Ahmad 32:981

'Abd al-Rahman narrated to us, 'Uzrah ibn Thabit al-Ansari narrated to us, from Thumamah ibn 'Abd Allah ibn Anas, that Anas used to breathe into the vessel twice or thrice. He said: And Anas claimed that the Messenger of Allah (peace and blessings of Allah be upon him) used to breathe into the vessel thrice.