He that toucheth pitch shall be defiled

This comes from the Apocrypha and is a warning against mixing with the rich. ‘As the wild ass is the lion’s prey in the wilderness, so the rich eat up the poor.’ In general it is a warning against wickedness. Keep company with evil men and soon you will be ‘tarred with the same brush’ – no more virtuous than they.

See also:

• He should have a long spoon that sups with the devil
• The rotten apple injures its neighbours
• Who keeps company with the wolf will learn to howl