Ash- Shaykh Muhammad bin Saalih Al -Uthaymeen (Rahimullaah) was asked the following question:
Question: What are the attributes of a friend you would advise (with)?
This is a important question. Friends have effect on the person who starts a friendship with them. About this was said, “Don’t ask about a person, but ask about his close friend, as every friend has an impact on his friend.”
In a correct hadeeth, the Prophet has compared the good companion with a person who has a musk. He either will give you some of it , or you will buy from him, or you will (at least smell) its fragrance. And the bad companion with who blows a furnace. He will either burn your clothes, or you will find an unpleasant smell coming from him. The Prophet said in a hadeeth: “a man follows the religion of his friend, so each one should consider whom he makes his friend”. Beware of bad friends! And keep on eager in goodness and righteousness . (Abu Dawud book 41#4815, Bukhari and Muslim)
(The good friends are) those who will help you in piety and that have taqwa of Allaah, and forbid you the immoral and the evil. And it is possible to test your friends; when you make friends with them for a week or ten days, you will know who is suitable and not suitable for friendship. Beware! Beware for making (friendship) with those who do not possess any goodness, whether it is because of their way of thinking, or aqeedah (belief), or aqlaaq (behaviour), or because of their worship.
And I ask Allaah to prepare righteous friends for you and us and Allaah has power over all things.