The following is the letter sent by Imam Ali (a) through Imam Husayn (a) and Ammar Yasir to the people of Kufa before he proceeded to Basra for the Batt  
This letter is from the servant and creature of Allah, Ali (a), Amir al-Mu'minin, to Kufiyites who are the leaders of Ansar and respectable persons. 
After praising Allah and invoking His Blessings on the Holy Prophet (s) I want to throw light on the event of the assassination of Uthman and to make the whole affair as clear as if you were present on the occasion and were witnessing the event yourself