The Heights - 7:86
Do not sit at the head of every path to pervert the way of Allah and to threaten the believers and turn them away from it. Think how He multiplied you when you were few in number. See how is the end of the corrupters.
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.