What saying best expresses the meaning of the moral in the fable about the farmer and the gray goose?

The saying that best expresses the moral of the fable about the farmer and the gray goose is "Don't kill the golden goose." This emphasizes the idea that one should not destroy a source of ongoing benefit for short-term gain. The farmer's greed leads to the loss of a consistent source of income, highlighting the importance of valuing what you have rather than risking it for immediate rewards.