After the Muslims took oath of allegiance to Imam Ali (a), he wrote the following letter to Mu’awiya. Waqidi has quoted this letter in his book, al-Jamal.
After glorifying Allah and praising the Holy Prophet (s) be it known to you that you very well know my attitude towards your tribe, why in the beginning I fought against you all in the defense of Islam and how and why later on I kept myself aloof from you and from your activities; I had no concern about your tribe till there took place the incident which could not be prevented. It is a long story and much has been said and is being said about it. However, that was to be. Now you take the oath of allegiance to me from the people of your province and come on deputation to me.