Sayyiduna Thabit bin al-Dahhak (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "Whoever falsely swears by a religion other than Islam is as he said; whoever kills himself with something will be punished with that very thing on the Day of Resurrection; and whoever calls a believer a disbeliever or curses him, that is equivalent to killing him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15876