Musannaf Ibn Abi Shayba 27:252

'Affan narrated to us, he said: Mu'awiyah ibn 'Abd al-Karim narrated to us, he said: Al-Hasan narrated to us that Dawud, the Prophet, peace be upon him, said: "My God, if every hair of mine had two tongues glorifying You night and day, we would not have fulfilled [the gratitude for] a blessing from Your blessings upon me."