Hadith: Verily, the example of the righteous companion and the evil companion is like that of the carrier of the musk and the blower of the bellows.

عَنْ أَبِي مُوسَى رضي الله عنه عَنِ النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ:
«إِنَّمَا مَثَلُ الْجَلِيسِ الصَّالِحِ وَالْجَلِيسِ السَّوْءِ كَحَامِلِ الْمِسْكِ وَنَافِخِ الْكِيرِ، فَحَامِلُ الْمِسْكِ: إِمَّا أَنْ يُحْذِيَكَ، وَإِمَّا أَنْ تَبْتَاعَ مِنْهُ، وَإِمَّا أَنْ تَجِدَ مِنْهُ رِيحًا طَيِّبَةً، وَنَافِخُ الْكِيرِ: إِمَّا أَنْ يُحْرِقَ ثِيَابَكَ، وَإِمَّا أَنْ تَجِدَ رِيحًا خَبِيثَةً».
[صحيح] - [متفق عليه] - [صحيح مسلم: 2628]

Abu Mūsa (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said:
"Verily, the example of the righteous companion and the evil companion is like that of the carrier of the musk and the blower of the bellows. The carrier of the musk will either give you, or you will buy from him, or you will get a pleasant smell from him, and the blower of the bellows will either burn your clothes or you will get an offensive smell."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Muslim - 2628]

Explanation

The Prophet (may Allah's peace and blessings be upon him) provided an example for two types of people:
First type: The righteous companion and friend who guides others to Allah and to what pleases Him and helps others obey Him. His example is like that of the musk seller who will either give you some thereof, or you will buy from him, or you will smell and get from him a pleasant fragrance.
Second type: The evil companion and friend who turns others away from the path of Allah and helps them commit sins, the one whom you see doing evil deeds and you receive criticism for being in his company. His example is like that of the blacksmith who blows his fire and either burns your clothes with the flying sparks of fire or you get a nasty smell from being close to him.