He mentioned the Khawarij and said about them, "Among them is a man with a deformed hand, or a stunted hand, or a small hand. Were it not that you might become arrogant, I would tell you what Allah has promised, on the tongue of Muhammad ﷺ, to those who kill them."I asked, "Did you yourself hear this from Muhammad ﷺ?"He replied, "Yes, by the Lord of the Kaabah. Yes, by the Lord of the Kaabah. Yes, by the Lord of the Kaabah."
و حدثنا محمد بن أبي بكر المقدمي حدثنا ابن علية وحماد بن زيد ح و حدثنا قتيبة بن سعيد حدثنا حماد بن زيد ح و حدثنا أبو بكر بن أبي شيبة وزهير بن حرب واللفظ لهما قالا حدثنا إسمعيل ابن علية عن أيوب عن محمد عن عبيدة
ذكر الخوارج فقال فيهم رجل مخدج اليد أو مودن اليد أو مثدون اليد لولا أن تبطروا لحدثتكم بما وعد الله الذين يقتلونهم على لسان محمد ﷺ قال قلت آنت سمعته من محمد ﷺ قال إي ورب الكعبة إي ورب الكعبة إي ورب الكعبة
Muslim narrated the hadith of Ubayda from Ali, the hadith of the Kharijites, and it has one of the most sahih and finest chains of transmission. It was narrated by Ayub, Qatada, Ibn Awn, Yunus, Hisham, Abu Amr bin Ala, Awf, Qurra, Jareer, Rabi bin Subayh, Muawiya bin Salih, and a group of others. Bukhari did not include it, and he has no excuse for leaving it out.
I say, Bukhari reported it through a different route than the one Daraqutni obligated him with, reporting it from the hadith of Suwayd bin Ghafla from Ali in Dalail Nubuwwah, volume 7, page 431, in part, and in Fadail Quran, volume 10, page 476, and in Istitabat Murtaddin, volume 15, page 314. It has already been established that Bukhari did not commit himself to reporting every sahih hadith. So there is no basis for holding him to it. And Allah knows best.