The Cow - 2:221
Do not marry women who associate partners unless they believe. A believing servant woman is better than a woman who associates partners, even if you like her. And do not marry your daughters to men who associate partners until they believe. A believing servant boy is better than one who associates partners, even if you like him. They call to the Fire. Allah, on the other hand, calls to Paradise and forgiveness, and He makes His verses clear to the people so that they may take admonition.
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.