Sahih Muslim Book 1, Hadith Number 204.

Chapter : Suicide is the gravest sin.

In the hadith narrated by Shu’ba the words are: Verily the Messenger of Allah (may peace be upon him) said: He who took an oath on a religion other than Islam as a liar would become so as he said, and he who slaughtered himself with a thing would be slaughtered with that on the Day of Resurrection.