Chapter 1: The Book of the Sunnah
' Ubaidah narrated from 'Ali bin Abu Talib,: That he mentioned the Khawarij, and said: "Among them there will be a man with a defective hand, or a short hand, or small hand. If you were to exercise restraint (i. e., not become overjoyed), I would tell you of what Allah has promised upon the lips of Muhammed for those who kill them." I (' Ubaidah) said: "Did you hear that from Muhammed?" He said: "Yes, by the Lord of the Ka' bah!' - three times."
Sunan Ibn Majah 167