Bukhari Vol 3. Hadith 267
Narrated by An Numan bin Bashir
The Prophet said "Both legal and illegal things are obvious, and in between
them are (suspicious) doubtful matters. So whoever forsakes those doubtful
things lest he may commit a sin, will definitely avoid what is clearly
illegal; and whoever 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."