The Cow - 2:285
"The Messenger believed in what was sent down to him from his Lord, and those who believed. They all believe in Allah, His angels, His Books and His messengers: "We make no distinction between any of His messengers."They say: "We have heard and obeyed. Our Lord, forgive us; to You is the return."
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.