Musannaf Ibn Abi Shayba 36:192

Sufyan ibn 'Uyaynah narrated to us, from 'Amr, from al-Hasan ibn Muhammad, that 'Ubayd Allah ibn Abi Rafi', the scribe of 'Ali, informed him that he heard 'Ali saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "He has indeed witnessed Badr," meaning Hatib ibn Abi Balta'ah. "And what makes you know? Perhaps Allah has looked upon the people of Badr and said: 'Do what you wish, for I have forgiven you.'"