"A person is known by the company he keeps...."

Rasulullah SAW has said "Do not have intimate companionship with anyone except a Muslim; and let only those who fear Allah partake of your meals"
(Al-Mishkaah)

In this hadith, Rasulullah SAW has indicated two guidelines:

1. There should be no intimate companionship with non-Muslims.
2. A good Muslim shoul avoid relationship with even imious Muslims.

It is indicated in another hadith that no one should enter your house except the pious (al-Kanz). The hadith could also mean that a Muslim should associate with non-Muslims only on necessity. There is an insistence in the hadith on keeping oneself in the company of the pious. A person is known by the company he keeps: association has its influence according to the characters of those who are associates; that is why Rasulullah SAW has warned against the entry of impious people in the house. Intimacy with such people is bound to have an adverse effect. Rasulullah SAW has said the company of the pious is like meeting a musk merchant; when one sits with him, he may give a small piece as a present and one can also buy musk from him; otherwise, at least he can enjoy the fragrance of musk while sitting with him. ad company has been likened to sitting near a blacksmith's furnace, where a spark may rise and burn one's clothes, if that does not happen, at least one will suffer from its bad smell and smoke.

(Mishkat al Masaabeeh)