The Family Of Imran - 3:52
"When Jesus sensed a disbelieving attitude from them, he said, "Who will help me in the way of Allah?"His disciples said, "We are God´s helpers; we have believed in God. Witness that we have become Muslims."
The most important criterion of belief:
The Cattle/6:82
Those who believe and do not mix their faith with wrongdoing, they deserve security and they have found the truth.
Luqman/31:13
"When Lokman advised his son, he said: "My dear son, do not associate partners with Allah; surely shirk (associating partners with God) is a great wrong."
The Companies/39:65
It has been revealed to you and those before you that if you associate partners, all that you do will be in vain and you will be of the losers.