Sahih Bukhari Volume 8, Book 78, Hadith Number 647.

Narated By Thabit bin Ad-Dahhak : The Prophet said, “Whoever swears by a religion other than Islam, is, as he says; and whoever commits suicide with something, will be punished with the same thing in the (Hell) Fire; and cursing a believer is like murdering him; and whoever accuses a believer of disbelief, then it is as if he had killed him.”