The Repentance - 9:28
O you who believe, the idolaters are unclean; let them not approach the Holy Mosque after this year. If you fear poverty, Allah will, if He wills, enrich you with His bounty. Allah is All-Knowing, All-Wise.
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.