The Light - 24:21
O you who believe, do not follow the steps of Satan. Whoever follows the steps of Satan, he commands to himself immorality and evil. Had it not been for Allah´s grace and mercy upon you, none of you would have been purified for ever. But Allah purifies those who will. Allah is All-Hearing, All-Knowing.
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.