In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Abu Hurairah [radiyallaahu-anhu] said, “The Messenger [sallal laahu alayhi wasallam] said, ‘A man is upon the religion of his bosom friend, so let one of you look to who he befriends’”.
Brief Reminder From This Hadeeth By Shaikh Zayd Bin Haadi Al-Madkhalee [rahimahullaah]
This hadeeth contains a Prophetic wisdom and a tremendous advice to the Muslims – that they accompany the best people and be distant from the evil people, for indeed the one who accompanies the best people will be [benefited] through good statements and deeds that are pleasing to Allaah [The Blessed and Exalted], and one’s status raised in the sight of Allaah. On the contrary, the one who accompanies evil people and his soul inclines towards them, he’ll earn abundant evil and turn away from good, and thus he’ll be a loser in this world, in the grave and in the afterlife.
Indeed, the Prophet [sallal laahu alayhi wasallam] gave an example regarding a good companion and an evil companion, saying: “The example of a good companion and a bad companion is like that of the seller of musk and the one who blows the blacksmith’s bellows. So, as for the seller of musk, then either he will grant you some, or you buy some from him, or at least you find a pleasant smell from him. As for the one who blows the blacksmith’s bellows, then either he will burn your clothes or you will get an offensive smell from him”.
So this hadeeth [i.e. a man is upon the religion of his companion] contains proof that a person is upon the religion of his bosom friend – the one he loves; upon the path of the one he loves, the one he sits with and speaks to [i.e. a friend]. Therefore, choose the most virtuous and the best of friends – the one who reminds you [i.e. about Allaah, your obligations etc] when you forget and encourage you.
[An Excerpt from At-ta’leeqaat Al-Maleehah Alaa Silsilah Al-Ahaadeeth As-Saheehah. Vol 1. Page17. Slightly paraphrased]