Musannaf Ibn Abi Shayba 33:770

Ibn ‘Uyaynah narrated to us, from ‘Amr, from ‘Ubayd ibn ‘Umayr, regarding the saying of Allah: "To every oft-returning (to Allah) and keeper (of His covenant)." He said: "It is the one who does not sit in a gathering, then stand up, except that he seeks the forgiveness of Allah."