Before he died, the Messenger of Allah ﷺ wrote to Khosrow, to Caesar, and to every tyrant ruler.
وكتب رسول الله ﷺ قبل أن يموت إلى كسرى وقيصر وإلى كل جبار
No references are available.
Its chain of transmission is hasan. It has already appeared at 13762.