Conspiracy to murder Uthman
When the country came to be rocked by agitation against Uthman, Ummair and Kammil entered into a conspiracy to murder Uthman. They accordingly decided to go to Madina with a view to assassinating Uthman. Ummair fell sick in the way, and he returned to Kufa. Kammil, however, decided to proceed to Madinah. In Madina, Kammil lay in ambush at a strategic point between the house of Uthman and the Prophet's mosque. One day as Uthman was proceeding to the mosque, he caught sight of Kammil lying in ambush under suspicious circumstances, and before Kammil could dare attack Uthman, Uthman attacked him with a lance in self defense and wounded him. Kammil cried "Amirul Mominin! you have wounded me for no cause." Uthman asked him to declare on oath whether he was not lying there in ambush to murder him. Kammil took the oath that he had no intention of murdering the Caliph. Men around Uthman wanted that a further probe should be made into the antecedents of Kammil so that his guilt could be determined. Uthman said that as Kammil had taken the oath in the name of God that he had no evil design, the matter rested with God and Kammil, and he would not make any further probe into the matter. He told Kammil that he could have his "Qasaas" from him for wounding him. Kammil said that in the circumstances, he freely forgave the Caliph, and withdrew his claim for "Qasaas." Thereafter Kammil returned to Kufa.

Siege of the house of Uthman
In spite of the magnanimity of Uthman, Kammil on return to Kufa continued his activities against Uthman. When in 656 C.E., a contingent from Kufa left for Madina, both Ummair and Kammil were included therein. When Uthman was assassinated Ummair and Kammil insisted that the dead body of Uthman should be mutilated. Years later when Hajjaj became the Governor of Kufa, he tried Ummair and Kammil for the murder of Uthman and had them executed.