The Repentance - 9:29
Fight those who believe not in Allah and the Last Day, nor forbid what Allah and His Apostle forbid, nor follow the true religion, from among those to whom the Book has been given, until they submit and pay a tax with their hands.
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.