From Sahih Muslim (Hadith 4914):
It has been reported on the authority of Bara! ' who stated:A man from Banu Nabit (one of the Ansar tribes) came to the Prophet (ﷺ) 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 Prophet (ﷺ) said: He has done a little but shall be given a great reward
Reference: Muslim 4914