Nahj al-Balāgha

Hadith 230
warfare-jihadhistorical-event
وقال (عليه السلام) لمّا عزم على حرب الخوارج وقيل له: إن القوم قد عبروا جسر النهروان
When Amīr al-mu’minīn showed his intention to fight the Khārijites he was told that they had crossed the bridge of Nahrawan and gone over to the other side. Amīr al-mu’minīn said :
Source: al-Sharīf al-Raḍī