Maliks Muwatta Book 21, Hadith Number 28.

Section : The Martyrs in the Way of Allah.

Yahya related to me from Malik from Abu’z-Zinad from al-Araj from Abu Hurayra that the Messenger of Allah, may Allah bless him and grant him peace, said, “Allah laughs at two men. One of them kills the other, but each of them will enter the Garden| one fights in the way of Allah and is killed, then Allah turns to the killer, so he fights (in the way of Allah) and also becomes a martyr.”