He who lends to a friend loses twice.
More French Proverbs:
A tender-hearted mother makes a scabby daughter.French
He who lies down with dogs gets up with fleas.
French
Princes keep good reckoning, they never lose anything.
French
You easily lend bread to the one who has flour.
French
It will not do to keep holidays before they come.
French
A churl never liked a gentleman.
French