Musnad Ahmad 5:668

Yazid narrated to us, Israel ibn Yunus informed us, from Thawr ibn Abi Fakhitah, from his father, from Ali ibn Abi Talib, who said: "Chosroes gifted the Messenger of Allah, may Allah bless him and grant him peace, and he accepted from him. Caesar gifted the Messenger of Allah, may Allah bless him and grant him peace, and he accepted from him. And the kings gifted, and he accepted from them."