Prophet Abraham - 14:11
"And their messengers said to them: "Surely we are human beings like you. But Allah chooses whom He wills from among His servants and bestows favor upon him. It is impossible for us to bring you a certificate of authority without Allah´s permission. Believers should trust in Allah."
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.