O you who believe! Believe in Allah, and His Messenger (Muhammad S), and the Book (the Qur'an) which He has sent down to His Messenger, and the Scripture which He sent down to those before (him), and whosoever disbelieves in Allah, His Angels, His Books, His Messengers, and the Last Day, then indeed he has strayed far away.
Surah (Chapter) an-Nisa” (The Women) The Qur-an 4:136

It may be that you (O Muhammad S) are going to kill yourself with grief, that they do not become believers [in your Risalah (Messengership) and in your Message of Islamic Monotheism].
Surah (Chapter) ash-Shu'ara” (The Poets) The Qur-an 26:3

And whosoever does not believe in Allah and His Messenger (Muhammad SAW), then verily, We have prepared for the disbelievers a blazing Fire.
Surah (Chapter) al-Fath (The Victory) The Qur-an 48:13