Midrash su Esodo 6:9

Therefore, say unto the children of Israel: “I am the Lord, and I will bring you out” (Exod. 6:6). The word therefore implies that an oath was involved, as it is said: Therefore I have sworn unto the house of Eli (I Sam. 3:14). Moses went to them and told them what the Holy One, blessed be He, had said: And Moses spoke so unto the children of Israel; but they harkened not unto Moses for impatience of spirit and for cruel bondage (Exod. 6:9). Whereupon Moses turned to the Holy One, blessed be He, saying: Behold, the children of Israel have not harkened unto me (ibid., v. 12). And the Lord said to Moses: “Go in, say unto Pharaoh, king of Egypt, that he let the children of Israel go” (ibid., v. 11). A proverb states: “There is no benefit to be derived from acacia wood except when it is cut down.”⁴An old proverb indicating that one must wait until an episode is concluded to learn the result. “Don’t count your chickens before they’re hatched.”