Musannaf Ibn Abi Shaybah

Hazrat Uqbah bin Aws as-Sadoosi, may Allah have mercy on him, narrates that Hazrat Abdullah bin Umar, may Allah be pleased with them both, said: There will be twelve (12) caliphs in this Ummah. Abu Bakr, may Allah be pleased with him, you people have already confirmed his name. And Umar bin Khattab, may Allah be pleased with him, who will be very trustworthy. You people have also confirmed his name. And Uthman bin Affan, may Allah be pleased with him, the possessor of two lights, who was entrusted with two responsibilities of mercy. And he was unjustly killed. You people have also confirmed his name.