Sunan Abu Dawud
4763
Sahih+3

‘Ubaidah (al-salman) said :‘Ali mentioned about the people of al Nahrawan, saying: Among them there will be a man with a defective hand or with a small hand. if you were not to overjoy. I would inform you of what Allah has promised (the reward for) those who will kill them at the tongue of Muhammad (May peace be upon him). I asked : Have you heard this from him? He replied : Yes, by the lord of the Ka’bah

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid