Abu Hurayrah (may Allah be pleased with him) said: No one is to be killed for reviling anyone, except for reviling the Prophet (peace and blessings be upon him).
Abu Ahmad (Ibn Adi) (may Allah have mercy on him) said: This hadith is known through Yahya bin Isma'il.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13378