Is a person considered an apostate if he curses or backbites someone who carries the name of a prophet, and he does so knowingly and attentively?

A Muslim must guard his tongue from insult and backbiting, for the Messenger of Allah, peace and blessings be upon him, said: "The believer is not a slanderer, nor a curser, nor an obscene individual, nor an indecent one." Insulting a Muslim without a legitimate Shar'i right is a major sin, for the Prophet, peace and blessings be upon him, said: "Insulting a Muslim is wickedness, and fighting him is disbelief."