Ubaydullah bin Abu Rafi reported,

When the Hururiyyah rebelled, Ubaydullah was with Ali bin Abu Talib, and they declared, "Judgment belongs to Allah alone."Ali responded, "A word of truth by which falsehood is intended. The Messenger of Allah ﷺ described certain people whose description I recognize in these very ones. They speak the truth with their tongues, but it does not pass beyond this," and he pointed to his throat. "They are among the most hateful of Allah's creation to Him. Among them is a black man, one of whose hands is like the teat of a sheep or the nipple of a breast."When Ali bin Abu Talib had killed them, he said, "Look for him."They searched but found nothing. So he said, "Go back. By Allah, I have not lied, nor have I been lied to," repeating this two or three times. Then they found him in a ruin, brought him, and placed him before Ali.Ubaydullah said, "I was present during this affair of theirs and during what Ali said about them."Yunus added in his narration, Bukayr said, "A man narrated to me from Ibn Hunayn that he said, 'I saw that black man.'"

عن عبيد الله بن أبي رافع مولى رسول الله ﷺ

أن الحرورية لما خرجت وهو مع علي بن أبي طالب قالوا: لا حكم إلا لله، فقال علي: كلمة حق أريد بها باطل، إن رسول الله ﷺ وصف ناسا إني لأعرف صفتهم في هؤلاء: يقولون الحق بألسنتهم لا يجوز هذا منهم وأشار إلى حلقه- من أبغض خلق الله إليه، منهم أسود، إحدى يديه طبي شاة أو حلمة ثدي، فلما قتلهم علي بن أبي طالب قال: انظروا، فنظروا فلم يجدوا شيئا، فقال: ارجعوا فوالله ما كذبت ولا كذبت، مرتين أو ثلاثا، ثم وجدوه في خربة، فأتوا به حتى وضعوه بين يديه، قال عبيد الله: وأنا حاضر ذلك من أمرهم وقول علي فيهم. زاد يونس في روايته: قال بكير: وحدثني رجل عن ابن حنين أنه قال: رأيت ذلك الأسود.