Sahih Muslim Book 19, Hadith Number 4426.

Chapter : The persecution of the Holy Prophet (may peace be upon him) at the hands of the infidels and hypocrites.

It has been narrated on the authority of Jundub b. Sufyan who said: A finger of the Messenger of Allah (may peace be upon him) was wounded in one of the encounters He said: Thou art just a little finger which has bled, and what thou hast experienced is in the cause of Allah.