The Cow - 2:26
"Allah does not hesitate to give the example of a mosquito or even the one on it. The believers know that this is a truth from their Lord. But the disbelievers say, "What did Allah intend by this analogy?"He leads many astray by it and guides many to the truth. He leads astray with it only the disbelievers."
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.