Musnad Ahmad 825:1

Yahya ibn Ishaq narrated to us, Yahya ibn Ayyub narrated to us, Yazid ibn Abi Habib narrated to us, from Rabi'ah ibn Laqit, from Abdullah ibn Hawalah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever is saved from three, he has been saved three times: my death, the Dajjal, and the killing of a Caliph who is patient with the truth, giving it its due."