The Coalition - 33:53
O you who believe, do not enter the house of the Messenger until you are called to eat. Nor wait for such a call. You may enter when you are called. After you have eaten, leave and disperse. Do not engage in hadiths (sayings). This grieved the Prophet, but he was ashamed to inform you. Allah is not ashamed to declare the truth. When you ask something of his wives, ask them behind a veil. This is purer for your hearts and their hearts. You must not grieve the Messenger of Allah and you must not marry his wives after him, for that is a great sin in the sight of Allah.
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.