Excerpts from Books and Wikipedia
"Ali and Uthman were the only serious candidates for the caliphate, but when the three days were up, no decision had been reached, so the chairman Abdul Rahman invited the congregation at morning prayers for their opinions. Because he appeared to have greater support, Abdul Rahman chose Uthman as caliph (r.644-656). A worldly and nepotistic caliph, Uthman's favors to his own clan led ultimately to rebellion, his own murder, and the beginning of the breakdown of Muslim unity." [1001 Days]