Musannaf Ibn Abi Shayba 37:367

Shababa narrated to us, from Layth ibn Sa'd, from Zayd ibn Abi Habib, from Rabi'ah ibn Laqit al-Tujibi, from Ibn Hawalah al-Azdi, from the Prophet (may Allah bless him and grant him peace) that he said: "Whoever is saved from three things has indeed been saved." He said it three times. They said: "And what are those, O Messenger of Allah?" He said: "My death, the Dajjal, and the killing of a Caliph who is patient upon the truth, [who] gives it [his due]."