Musnad Ahmad 25:764

Ahmad ibn Abd al-Malik al-Harrani narrated to us, he said: Yahya ibn Amr ibn Malik al-Nukri narrated to us, he said: I heard my father narrating from Abu al-Jawza’, from Ibn Abbas, he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The expiation for a sin is remorse." And the Messenger of Allah, may Allah bless him and grant him peace, said: "If you were not to commit sins, Allah, the Almighty and Majestic, would bring a people who would commit sins, so that He might forgive them."