According to rahyafte (the missionaries and converts website) A person went to Imam al-Sadiq (a) and said,
“O Son of the Prophet (a)! I heard that your cousin insulted and slandered you.”
When he finished his talk, Imam al-Sadiq (a) began performing prayer. That talebearer thought that Imam (a) would curse his cousin in the prayer; but, contrary to his expectation, after Imam (a) finished the prayer, supplicated to God, “O My Lord! I forgave him; and Your generosity is greater than mine; so, forgive him and do not punish him for this action of his.”
By hearing this supplication, that talebearer got up in shame and wentThis is among the conducts of the Ahl al-Bayt (a) of the honorable Prophet (a) toward their enemies. By seeing such beautiful manners of the Ahl al-Bayt (a), we learn that God(Allah) knows whom He assigns with the prophethood and imamate and whom He appoints as His proof and vicegerent among His creation.
Jami‘ al-Ahadith al-Shi’a, vol. 7, p. 457, hadith no. 36.