From Sahih Muslim (Hadith 4894):
It has been reported on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said: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
Reference: Muslim 4894