It is not a pain to give to ingrates, but it is an intolerable one to be obliged to a dishonest man.
Ce n'est pas un grand malheur d'obliger des ingrats, mais c'en est un insupportable d'être obligé à un malhonnête homme.
Original text (French)
Variants
It is not a great misfortune to be of service to ingrates, but it is an intolerable one to be obliged to a dishonest man.