Sahih Muslim 1066 g
'Ubaidullah b. Abu Rafi', the freed slave of the Messenger of Allah (ﷺ), said:
When Haruria (the Khawarij) set out and as he was with 'Ali b. Abu Talib (Allah be pleased with him) they said, "There is no command but that of Allah." Upon this 'Ali said: The statement is true but it is intentionally applied (to support) a wrong (cause). The Messenger of Allah (ﷺ) described their characteristics and I found these characteristics in them. They state the truth with their tongue, but it does not go beyond this part of their bodies (and the narrator pointed towards his throat). The most hateful among the creation of Allah is one black man among them (Khawarij). One of his hand is like the teat of a goat or the nipple of the breast. When 'Ali b. Abu Talib (Allah be pleased with him) killed them, he said: Search (for his dead body). They searched for him, but they did not find it (his dead body). Upon this he said: Go (and search for him). By Allah, neither I have spoken a lie nor has the lie been spoken to me. 'Ali said this twice and thrice. They then found him (the dead body) in a rain. They brought (his dead) body till they placed it before him (Hadrat 'Ali). 'Ubaidullah said: And, I was present at (that place) when this happened and when 'Ali said about them. A person narrated to me from Ibn Hanain that he said: I saw that black man.
حَدَّثَنِي أَبُو الطَّاهِرِ، وَيُونُسُ بْنُ عَبْدِ الأَعْلَى، قَالاَ أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ وَهْبٍ، أَخْبَرَنِي عَمْرُو بْنُ الْحَارِثِ، عَنْ بُكَيْرِ بْنِ الأَشَجِّ، عَنْ بُسْرِ بْنِ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ أَبِي رَافِعٍ، مَوْلَى رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّ الْحَرُورِيَّةَ لَمَّا خَرَجَتْ وَهُوَ مَعَ عَلِيِّ بْنِ أَبِي طَالِبٍ - رضى الله عنه - قَالُوا لاَ حُكْمَ إِلاَّ لِلَّهِ ‏.‏ قَالَ عَلِيٌّ كَلِمَةُ حَقٍّ أُرِيدَ بِهَا بَاطِلٌ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم وَصَفَ نَاسًا إِنِّي لأَعْرِفُ صِفَتَهُمْ فِي هَؤُلاَءِ ‏
"‏ يَقُولُونَ الْحَقَّ بِأَلْسِنَتِهِمْ لاَ يَجُوزُ هَذَا مِنْهُمْ - وَأَشَارَ إِلَى حَلْقِهِ - مِنْ أَبْغَضِ خَلْقِ اللَّهِ إِلَيْهِ مِنْهُمْ أَسْوَدُ إِحْدَى يَدَيْهِ طُبْىُ شَاةٍ أَوْ حَلَمَةُ ثَدْىٍ ‏"‏ ‏.‏ فَلَمَّا قَتَلَهُمْ عَلِيُّ بْنُ أَبِي طَالِبٍ - رضى الله عنه - قَالَ انْظُرُوا ‏.‏ فَنَظَرُوا فَلَمْ يَجِدُوا شَيْئًا فَقَالَ ارْجِعُوا فَوَاللَّهِ مَا كَذَبْتُ وَلاَ كُذِبْتُ ‏.‏ مَرَّتَيْنِ أَوْ ثَلاَثًا ثُمَّ وَجَدُوهُ فِي خَرِبَةٍ فَأَتَوْا بِهِ حَتَّى وَضَعُوهُ بَيْنَ يَدَيْهِ ‏.‏ قَالَ عُبَيْدُ اللَّهِ وَأَنَا حَاضِرُ ذَلِكَ مِنْ أَمْرِهِمْ ‏.‏ وَقَوْلِ عَلِيٍّ فِيهِمْ زَادَ يُونُسُ فِي رِوَايَتِهِ قَالَ بُكَيْرٌ وَحَدَّثَنِي رَجُلٌ عَنِ ابْنِ حُنَيْنٍ أَنَّهُ قَالَ رَأَيْتُ ذَلِكَ الأَسْوَدَ ‏.‏