The Women - 4:162
Only those among them who have knowledge and those who believe believe in what has been sent down to you and what was sent down before you. They observe prayer and pay the zakat and believe in Allah and the Last Day; to them We shall give a great reward.
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.