The Table Spread - 5:106
"Believers, when death comes to one of you, let two just witnesses be present from among you at the time of the will. And if death comes to you while you are traveling, two of you who are not of you. If you are in doubt, detain the witnesses after the prayer and say in the name of Allah: "We will not exchange our testimony for anything, not even relatives, nor conceal the testimony of Allah. Otherwise, we shall be among the sinners."
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.