It is narrated from Sayyiduna Thabit bin al-Dahhak (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever swears falsely by a religion other than Islam, he is as he said; and whoever kills himself with something will be punished with it in the fire of Hell; and cursing a believer is like killing him; and whoever accuses a believer of disbelief, it is like killing him."
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1313