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