The Messenger of Allah ﷺ said, "The example of a good companion and a bad companion is like that of the seller of musk and the blacksmith's bellows. As for the seller of musk, you will not fail to benefit from him. Either you will buy some musk, or you will catch its pleasant scent. As for the blacksmith's bellows, they will either burn your body or your clothes, or you will smell from them a foul stench."
قال رسول الله ﷺ: مثل الجليس الصالح والجليس السوء كمثل صاحب المسك وكيرالحداد، لا يعدمك من صاحب المسك: إما تشتريه، أو تجد ريحه. وكير الحداد يحرق بدنك أو ثوبك، أو تجد منه ريحا خبيثة.
Bukhari related it in the Book of Business Transactions (2101), and Muslim in the Book of Virtue and Kinship (2628), both through Burayd bin Abdullah (that is, Ibn Abu Burda bin Abu Musa Ashari), from his grandfather Abu Burda bin Abu Musa Ashari, from Abu Musa Ashari, who related it.