The Cow - 2:249
"When Talut took command of the army, he reported: "Allah will test you with a river. Whoever drinks from it is not from me. Whoever does not taste it but only takes a sip with his hand is from me."They all drank from it except a few. When he crossed the river with those who believed with him, they said, "Today we have no strength to resist Goliath and his army."And those who believed that they would meet Allah said: "How many a small company has defeated a large company by Allah´s permission. Allah is with the patient."
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.