Sahih Muslim Book 5, Hadith Number 2316.

Chapter : Exhortation to kill the Khwarij.

Jabir b. Abdullah reported that a person came to the Messenger of Allah (may peace be upon him) at Jirana on his way back from Hunain, and there was in the clothes of Bilal some silver. The Messenger of Allah (may peace be upon him) took a handful out of that and bestowed it upon the people. He (the person who had met the Prophet at Jirana) said to him: Muhammad, do justice. He (the Holy Prophet) said: Woe be upon thee, who would do justice if I do not do justice, and you would be very unfortunate and a loser if I do not do justice. Upon this Umar b. Khattab (Allah be pleased with him) said: Permit me to kill this hypocrite. Upon this he (the Holy Prophet) said: May there be protection of Allah ! People would say that I kill my companions. This man and his companions would recite the Qur’an but it would not go beyond their throat, and they swerve from it just as the arrow goes through the prey.