Musnad Ahmad 1034:121

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, he said: I heard Abu Ishaq, he said: I heard al-Walid Abu al-Mughirah, or al-Mughirah Abu al-Walid, narrating that Hudhayfah said: O Messenger of Allah, I have a sharp tongue, and most of that is directed toward my family. He said: "Where are you regarding seeking forgiveness (istighfar)?" He said: "I indeed seek forgiveness in the day and the night, or in the day, one hundred times."