The Family Of Imran - 3:199
Among the People of the Book are those who believe in Allah and what has been sent down to you and what has been sent down to them. They have deep respect for Allah. They do not sell the Verses of Allah for a small price. Their reward is with their Lord. Allah is quick in reckoning.
The most important criterion for believing in Allah:
The Cattle/6:82
Those who believe and do not mix their faith with wrongdoing, they deserve security and they have found the truth.
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.
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."