Abu Kathir reported,

I was with my master Ali bin Abu Talib at the place where the people of Nahrawan were killed. The people seemed troubled within themselves over having killed them.Ali said, "People, the Messenger of Allah ﷺ told us about a group who would pass through the religion as an arrow passes through its target, never returning to it until the arrow returns to its notch. The sign of this is that among them is a black man with a deformed arm. One of his arms is like a woman's breast, with a nipple like a woman's nipple, surrounded by seven hairs. Search for him, for I believe he is among them."So they searched for him and found him at the riverbank beneath the slain. They pulled him out, and Ali said the takbir and exclaimed, "Allah is greatest! Allah and His Messenger have spoken the truth!"He was wearing an Arabian bow slung across his shoulder. He took it in his hand and began prodding the man's deformed arm with it, saying, "Allah and His Messenger have spoken the truth."The people said the takbir when they saw him and rejoiced, and what they had been feeling left them.

حدثنا أبو سعيد مولى بني هاشم حدثنا إسماعيل بن مسلم العبدي

حدثنا أبو كثير مولى الأنصار قال

كنت مع سيدي علي بن أبي طالب رضي الله عنه حيث قتل أهل النهروان فكأن الناس وجدوا في أنفسهم من قتلهم فقال علي رضي الله عنه يا أيها الناس إن رسول الله ﷺ قد حدثنا بأقوام يمرقون من الدين كما يمرق السهم من الرمية ثم لا يرجعون فيه أبدا حتى يرجع السهم على فوقه وإن آية ذلك أن فيهم رجلا أسود مخدج اليد إحدى يديه كثدي المرأة لها حلمة كحلمة ثدي المرأة حوله سبع هلبات فالتمسوه فإني أراه فيهم فالتمسوه فوجدوه إلى شفير النهر تحت القتلى فأخرجوه فكبر علي رضي الله عنه فقال الله أكبر صدق الله ورسوله وإنه لمتقلد قوسا له عربية فأخذها بيده فجعل يطعن بها في مخدجته ويقول صدق الله ورسوله وكبر الناس حين رأوه واستبشروا وذهب عنهم ما كانوا يجدون