Musnad Ahmad 33:489

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu al-Zubayr narrated to us, from Jabir, who said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "The servant is with whom he loves." And the Messenger of Allah, may Allah bless him and grant him peace, wrote before he died to Chosroes, to Caesar, and to every tyrant.