Abu Musa relates that Allah’s Messenger (peace and blessings of Allah be to him) said, “The example of a good companion (who sits with you) in comparison with a bad one, is like that of the musk seller and the blacksmith’s bellows (or furnace); from the former you would either buy musk or enjoy its good smell while the bellows would either burn your clothes or your house, or you get a bad nasty smell thereof.” (Sahih al-Bukhari)
A man is known by the company he keeps. A wise person is very much selective in establishing friendship. He considers the merits and demerits of a new person and envisions the pros and cons of the new friendship.
This hadīth highlights the merits of a good companion and distinguishes them from those of a bad one. The similes of the musk seller’s good smell and the blacksmith’s bellows make the distinction palpably evident. If a person enjoys the company of a musk seller, he would buy musk, or at least enjoy its good smell. Thus such friendship is a continuous source of joy even at no cost.
A bad companion is likened as a blacksmith’s furnace. A furnace either burns one’s clothes or house or at least gives him bad smell. Similarly, in the company of a bad companion one is always in the danger of picking bad habits, indulging in indecent talks, etc. or at least earning a bad name. Hence the moral that man should always keep the company of good friends and shun that of bad ones.