Sahih Muslim Book 20, Hadith Number 4679.

Chapter : In proof of the martyr’s attaining paradise.

It has been reported on the authority of Bara!’ who stated: A man from Banu Nabit (one of the Ansar tribes) came to the Holy Prophet (may peace be upon him) and said: I testify that there is no god except Allah and that thou art His bondman and Messenger. Then he went forward and fought until he was killed. The Holy Prophet (may peace be upon him) said: He has done a little but shall be given a great reward.