Musannaf Ibn Abi Shayba 37:637

Waki’ narrated to us, from Yazid ibn Mardanbah, from Khalifah ibn Sa’id, who said: I saw Uthman in one of the paths of Medina, and he was saying: "Enjoin the good and forbid the evil before the worst among you are empowered over you, then the best among you will supplicate against them, and it will not be answered for them." He said: And I jostled him, so he took hold of my upper arms and said: "I will not die until the leadership of the boys reaches me."