It is narrated from Sayyiduna Thabit bin al-Dahhak (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Cursing a believer is like killing him; and whoever declares a Muslim a disbeliever, then one of the two has earned it."
Imam Abu al-Qasim (al-Tabarani) (may Allah have mercy on him) said: By "Abu Abdullah" is meant Khalid al-Hadhdha' himself, and Khalid had two kunyas: Abu Munazil and Abu Abdullah.
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1327