Isa bin Yazid said: Al-Ash'ath (may Allah be pleased with him) sought permission (to visit) Mu'awiyah (may Allah have mercy on him) in Kufah, and he kept him waiting for a long while, while Sayyiduna Ibn Abbas and Sayyiduna al-Hasan bin Ali (may Allah be pleased with them both) were with him. Al-Ash'ath said: O Commander of the Believers! Is it because of these two that you kept me waiting? You know that their companion (meaning Sayyiduna Ali (may Allah be pleased with him)) came to us and filled us with lies. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Do you think I would revile you by means of Ibn Abi Talib? Al-Ash'ath said: No Arab better than me has ever been reviled. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: (As for you,) a slave of Mahrah killed your grandfather and speared your father in his backside. At that al-Ash'ath said (to Mu'awiyah): Do you not hear what he is saying to me, O Commander of the Believers? Mu'awiyah said: It was you who started it.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 649