Be advised that all flatterers live at the expense of those who listen to them.
Apprenez que tout flatteur
Vit aux dépens de celui qui l'écoute.
Vit aux dépens de celui qui l'écoute.
Original text (French)
Source, in full
Book I (1668), fable 2. Variant translations: Learn now that every flatterer lives at the cost of those who give him credit. / In exchange for your cheese I will give you a piece of advice for the future — Do not trust flatterers. / Every flatterer lives at the expense of him who listens to him.