Divorce - 65:2
When they have fulfilled their term, keep them well, or separate them well. And take two just men from among you as witnesses. Bear witness for the sake of Allah. This is an admonition for those who believe in Allah and the Last Day. And whoever listens to Allah, He will create for him a way out.
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."