Nahj al-Balagha
Ali writes, in the "Nahj al-Balagha", that he was blamed by the Umayyads for the assassination of Uthman.The Umayyads knowledge of me did not restrain them from accusing me, nor did my precedence in accepting Islam keep these ignorant people from blaming me. Allah's admonitions are more eloquent than my tongue. I am the contester against those who break away from Faith and the opposer of those who entertain doubts. Uncertainties should be placed before Qur'an, the Book of Allah (for clarification). Certainly, people will be recompensed according to what they have in their hearts. – "Nahj al-Balagha: Sermon 75"