The Messenger of Allah ﷺ wrote to Caesar and said, "If you turn away, then upon you will be the sin of the Arisiyyin."
أن رسول الله ﷺ كتب إلى قيصر وقال: فإن توليت فإن عليك إثم الأريسيين.
Bukhari narrated it in the Book of Jihad and Expeditions (2936), from Ishaq, who said, Yaqub bin Ibrahim told us, the nephew of Ibn Shihab told us, from his uncle, who said, Ubaydullah bin Abdullah bin Utba bin Masud told me, and he mentioned it.