Volume 3, Book 34, Number 267:
Narrated An-Nu’man bin Bashir (radiallaahu `anhu):
The Prophet (sallallaahu `alayhi wasallam) said “Both legal and illegal things are obvious, and in between them are (suspicious) doubtful matters. So who-ever forsakes those doubtful things lest he may commit a sin, will definitely avoid what is clearly illegal; and who-ever indulges in these (suspicious) doubtful things bravely, is likely to commit what is clearly illegal. Sins are Allah’s Hima (i.e. private pasture) and whoever pastures (his sheep) near it, is likely to get in it at any moment.”
This Hadith has been mentioned before but Imaam Bukhari brings it again under the Book of Sales and Trade to make a point of the fact that our sharee`ah defines the halal and haram of business and trade very clearly. But then there are some things which are doubtful – whoever indulges in them knowingly, feeling sure of himself, will fall into sin. So it’s better to avoid the grey area and save yourself from sin.