Nu’man bin Bashir relates: I heard Allah’s Messenger (peace and blessings of Allah be to him) as having said this (and Nu’man pointed his fingers towards the ears): What is lawful is evident and what is unlawful is evident, and 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 listen it is the heart.
(Sahih Muslim)
Allah has clearly defined what is lawful and what is unlawful. In between these there lie the doubtful. The person who avoids the use of the doubtful guards himself against falling into pitfalls. For the use of the doubtful paves the way for falling into the net of evil.
The Holy Messenger (peace and blessings of Allah be to him) has explained the process of moral deterioration with the help of a simile of a king’s preserve. The shepherd, who does not keep his sheep from the preserve, hazards misfortune. True believers are cautioned not to go near the doubtful lest they should be tempted to cross the Rubicon.