The Table Spread - 5:54
Believers, whoever turns away from his religion, know this: Allah brings a people whom He loves, and they love Him. They are humble towards the believers and strong and firm against the disbelievers. They strive hard in the way of Allah and do not fear the condemnation of those who condemn. This is the bounty of Allah; He gives it to whom He wills. Allah is Generous, 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.