Salamu alaykum Shaykh, is it allowed to transmit hadiths from khawarijs? Is it true that Imam Bukhari, rahimahullah transmitted hadiths from khawarij?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

If you mean "Is it permissible to narrate a Hadeeth if one of its narrators is from the Khawaarij," then the answer is that the scholars differed in opinion about the permissibility of this; some of them forbade it and some permitted it, because the Khawaarij do not consider it lawful to lie; in fact, they believe that one who lies exits the fold of Islam. Therefore, it can be assured that they do not lie in their accounts. Imaam Abu Daawood the author of the Sunan, said: "There is no one among the people who follow their desires more truthful when they narrate the Hadeeth than the Khawaarij."

The Fiqh Encyclopedia reads: "Abu Haneefah, Ash-Shaafi‘i, Yahya ibn Sa‘eed, ‘Ali ibn Al-Madeeni and others permitted narrating from the people who follow their desires if they were known to be truthful and they were not suspected of lying like the Khawaarij, but not those who are suspected of lying among the people who follow their desires." [End of quote]

It is for this reason that Imaam Al-Bukhari reported from some Khawaarij who are described as mastering the memorization of the Hadeeth because they do not lie. Shaykh Al-Islam Ibn Taymiyyah said (in his book Minhaaj As-Sunnah An-Nabawiyyah): "The Khawaarij hardly lie; in fact, they are the most truthful among the people despite the fact that they follow innovation and misguidance."

Shaykh Al-Islaam also said: "There is none among the people who follow desires who are more truthful and more devout in worship than the Khawaarij; Ahl As-Sunnah deal with them with justice and equity and they do not wrong them."

Allaah Knows best.