I am given to understand that Mu'awiya has been corresponding with you. Beware, he wants to make a fool of you, to blunt your intelligence and to harm your self-respect. Remember that it is Satan which will attack an imprudent and incautious Muslim from behind and from right and left so that finding him unwary and unwatchful, it may overpower him and may enslave his reasoning.
The fact is that during the Caliphate of Caliph Umar, Abu Sufyan unwisely gave utterances to something which was unjustifiable and unreasonable. It was one of those evil suggestions of Satan which are not only an insult to a self-respecting man but which cannot help in proving the descent (according to the laws of Islam) or in legalizing the heritage. The condition of a man claiming such a lineage is that of a gate crasher in a party from which he may be thrown out with humiliation.

Ziyad was the son of a slave named Ubayd, his mother was Sumaiyya, a slave-girl of Haarith bin Kalda, a woman of flexible virtues and very elastic conscience. But Ziyad grew up to be an intelligent man and a very good orator. Everybody knew that Ziyad was born out of wedlock. Umar during his caliphate, did not give him any chance but later on he became a governor and Imam Ali (a) had allowed him to retain that post. When Mu'awiya came to power, he started corresponding secretly with Ziyad, inviting him to leave the side of Imam Ali (a) and to join him, offering him the bribe of being declared the son of Abu Sufyan. When Imam Ali (a) came to know of these secret messages he wrote the following letter to Ziyad.