Sahih Muslim Book 1, Hadith Number 174.

Chapter : Prohibition of killing of an infidel after he say’s: “There is no god but Allah”.

The same hadith has been transmitted by the same chain of narrators. The hadith transmitted by Auza’i and Ibn Juraij contains these words: I embraced Islam for Allah’s sake, and in the hadith narrated by Ma’mar the words are: I knelt down to kill him, that he said; There is no god but Allah.