The Spoils of War - 8:72
Those who believe and migrate in the Way of Allah and strive hard with their wealth and their lives and those who shelter them and help them are friends of one another. Those who believe but do not emigrate with you, you are not responsible for them until they emigrate. But if they ask you for help on account of their religion, you should help them, provided it is not against a people with whom you have an agreement. Allah is All-Seeing of what you do.
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.