مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2608
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: "The expiation for sin is regret.” And the Messenger of Allah (ﷺ) said: “If you did not sin, Allah, may He be glorified and exalted, would bring another people who would commit sin so that He could forgive them.”
Musnad Ahmad 2623Hasan because of corroborating evidence; its isnad is da'eef