Musnad Ahmad 929:7

Muhammad ibn ‘Amr ibn al-‘Abbas al-Bahili narrated to us, Sufyan narrated to us, from ‘Asim, from Abu ‘Uthman, from Ubayy: That a man boasted of his lineage, so Ubayy told him to bite his father’s private part. They said, "You were never one to use foul language." He said, "We have been commanded to do that."