An announcement about what took place in Siffin
Nahj al-Balāgha|Volume 1|Book 2|Chapter 58
ومن كتاب له (عليه السلام) كتبه إلى أهل الأمصار يقتص فيه ما جرى بينه وبين أهل صفين
Written to the people of various localities describing what took place between him and the people of Ṣiffīn.