מדרש אויף בראשית 26:31

And it came to pass, when Pharaoh had let the people go (Exod. 13:17). The word let go (shallah) indicates “to escort,” as in the verse Abraham went with them to bring them (leshalleham) on the way (Gen. 18:16). Similarly it states; And Isaac sent them away (vaye-shallehem), and they departed from him in peace (ibid. 26:31). Why does this scriptural portion open with this verse? Because the mouth (i.e., Pharaoh) that had declared: And moreover, I will not let Israel go (Exod. 5:2), now retracted and said: I will let you go (ibid. 8:24). This explains why this portion of Scripture begins with the words When Pharaoh had let the people go. What was his reward for doing so? Thou shalt not abhor an Egyptian (Deut. 23:8), for the mouth that had said: I know not the Lord (Exod. 5:2) reversed itself and declared: The Lord is righteous (ibid. 9:27). What was his reward for saying this? He gave them a burial place, as it is said: Thou stretchest out Thy right hand—the earth swallowed them (ibid. 15:12).

(Exodus 13:17) "And it was, when G–d sent ("shalach") the people": "sending" in all places is accompaniment, viz. (Genesis 18:16) "And Abraham went with them to send them," (Ibid. 26:31) "And Israel sent them." The mouth (of Pharaoh) that said (Exodus 5:2) "Israel, too, I will not send," it is that (mouth) which said (Ibid. 10:10) "I will send you and your children." How was he rewarded for this? (Devarim 23:8) "You shall not abominate an Egyptian." The mouth which said (Exodus 5:2) "I do not know the L–rd," it is that (mouth) which said (Ibid. 14:25) "I will flee from before Israel, for the L–rd wars for them against the Egyptians." How was he rewarded for this? (Isaiah 19:19) "On that day there will be an altar to the L–rd in the midst of the land of Egypt and a pillar at its border to the L–rd." The mouth which said (Exodus 5:2) "Who is the L–rd that I should hearken to His voice," it is that mouth which said (Ibid. 9:27) "the L–rd is the Tzaddik, and I and my people are the wicked" — wherefore He gave them a place for burial, as it is written (Ibid. 15:12) "You inclined Your right hand — the earth swallowed them up."