The Muslim's Piety and Self Restraint
From an-Nu'maan ibn Basheer (radiyallaahu 'anhu) who said that I heard Allaah's Messenger (salallaahu 'alaihi wa'sallam) say:
That which is lawful is clear, and that which is forbidden is clear, and between them are doubtful matters about which many of the people have no knowledge. So whoever avoids doubtful matters saves his Religion and his honour, and whoever falls into doubtful matters falls into what is forbidden. Just like a shepherd who grazes (his sheep) near to a private pasture (of another), he will soon stray on to it. Indeed for every king there is a private preserve. Indeed the preserve of Allaah are those things which He has forbidden. Indeed there is a piece of flesh in the body which if it is good, then the whole body is good, but if it is corrupt then the whole body is corrupt. Indeed it is the heart. 
So the Muslim with regard to whatever situation arises in his life will have to face each of them with one of the following three stances:
Completely refraining from it: That is with regards to that which is doubtful Accepting without constraint: That is with regard to which is clearly permissible
To abstain from it: This is with regards to things which are not clearly permissible nor clearly forbidden. If the last stance indicates something it is an indication of a Muslim's piety and fear of falling into that which is forbidden and of entering into something evil.
The Muslim therefore abstains from it, and distances himself from it in order to please Allaah and to ensure that His commands are followed. It is not to be said, as some people say: 'That is not forbidden, so do it.' No, since it is not permissible to do everything other than which has been forbidden. So those things which are doubtful matters are closer to that which is forbidden, as occurs in the hadeeth itself: 'Whoever falls into the doubtful matters falls into what is forbidden....' So this fear and piety confirms that: