Musnad Ahmad 30:2679

Yazid narrated to us, he said: Muhammad ibn ‘Amr informed us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Verily, I seek forgiveness from Allah, the Almighty and Majestic, and I repent to Him one hundred times every day."