The Apartments - 49:11
O you who believe, let not one community mock at another community, lest they be better than themselves. And let not women mock at women; perhaps they are better than themselves. And do not reproach one another and do not call one another by derogatory words. What an evil name is to go astray after faith. Whoever does not repent, they are the wrongdoers.
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.