The same tradition has been narrated on the authority of Abu Zinad (with the same chain of transmitters).
Sahih Muslim Book 33, Hadith 189
← Previous Hadith God laughs at the two men both of whom will enter Paradise (though) one of them kills the other. They said: Messenger of Allah, how is it? He said: One of them fights in the way of Allah, the Almighty and Exalted. and dies a martyr. Then God turns in mercy to the murderer who embraces Islam, fights in the way of Allah, the Almighty and Exalted, and dies a martyr.

Sahih Muslim Book 33, Hadith 188 Next Hadith → God laughs at the two men one of whom kills the other; both of them will enter Paradise. They (the Companions) said: How, Messenger of Allah? He said: One is slain (in the way of Allah) and enters Paradise. Then God forgives the other and guides him to Islam; then he fights in the way of Allah and dies a martyr.

Sahih Muslim Book 33, Hadith 190