Nu’man bin Bashir reports: I heard Allah’s Messenger (peace and blessings of Allah be to him) as having said this (and Nu’man pointed towards his ears with his fingers): What is lawful is evident and what is unlawful is evident, and what is in between them are the things doubtful which many people do not know. So he who guards against doubtful things keeps his religion and honour blameless, and he who indulges in doubtful things indulges in fact in unlawful things, just as a shepherd who pastures his animals round a preserve will soon pasture them in it. Beware, every king has a preserve, and the things God has declared unlawful are His preserves. Beware, in the body there is a piece of flesh; if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt, and it is the heart.”
(Sahih Muslim)
Allah has clearly defined what is lawful and what is unlawful. In between these there lie certain things which are doubtful. The man who shuns doubtful things guards himself against pitfalls, since the use of doubtful things paves the way for falling into the net of evil. One starts doing what apparently has no evil, but the intention behind it is no good. He then proceeds slowly and steadily on this dangerous path without realising the enormity of danger lying ahead, and ultimately falls victim to evil. The Blessed Messenger has explained this deterioration with the help of the simile of a king’s preserve.