Musnad Abu Ya'la al-Mawsili 115:148

Ahmad ibn al-Miqdam al-'Ijli narrated to us, Mu'tamir narrated to us, he said: I heard my father narrating from Qatadah, from Anas, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, I seek forgiveness seventy times in a day."