It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Holy Prophet (peace and blessings of Allah be upon him) said: Allah Almighty smiles at two men, one of whom killed the other, but both of them enter Paradise. The explanation of this is that one man was a disbeliever; he martyred a Muslim, but before his own death, that disbeliever also accepted Islam, and Allah Almighty granted both of them entry into Paradise.