The Woman Who Is Examined - 60:4
"There is a good example for you in Abraham and those who were with him. Those who were with him said to their people, "We are far from you and those whom you serve besides Allah. We do not know you. There is eternal enmity and hatred between us and you until you believe in Allah ALONE. Except that Abraham´s words to his father, "I will pray for your forgiveness, but I cannot protect you against anything from Allah"(as a mistake). "Our Lord, to You we trust, to You we turn, and to You we shall return."
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.