The Light - 24:58
O you who believe, those who work under you and those of you who have not yet reached puberty should take permission three times: Before the Fajr prayer, at noon when you take off your clothes to rest, and after the Evening prayer. These are your three special times. Other than these, there is no harm in going in and out of each other´s company. This is how Allah explains the verses to you. Allah is All-Knowing, All-Wise.
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.