Midras Mazmur 147:15: Shemot Rabbah & Pesikta Rabbati

Another matter, “it was when Pharaoh let the people go” – that is what is written: “He sends His command to earth” (Psalms 147:15). Woe is the wicked, as they are maggots and worms and [will be] eliminated from the world, yet they seek to abrogate the word of the Holy One blessed be He. He said to them: ‘You said: “And I will not let Israel go” (Exodus 5:2), but I said: “Let My people go” (Exodus 5:1) – let us see whose word stands and whose word is void.’ Ultimately, Pharaoh himself arose, went, and fell at the feet of Moses, and said to Israel: “Arise and depart” (Exodus 12:31). The Holy One blessed be He said to him: ‘What then, Pharaoh, did your word stand, or My word?’ That is why it is stated: “He sends His command to earth.” When? “It was when Pharaoh let the people go.”
Did Pharaoh let them go? Bilam said: “God, who took them out of Egypt” (Numbers 24:8), and here it says: “It was when Pharaoh let the people go”? Rather, it teaches that Pharaoh was accompanying them, and saying to them: ‘Pray and beg for mercy for me,’ as it is stated: “Take both your flocks and your herds, as you said, and go; and bless me, too” (Exodus 12:32). Letting them go [shiluaḥ] stated here means nothing other than accompaniment, as it is stated: “Abraham went with them to see them off [leshalleḥam]” (Genesis 18:16).

... Another explanation: “O poor tempestuous one, who was not consoled…” (Isaiah 54:11) R’ Levi said any where that it says she does not have, she has. It is written “…that is Zion whom no one seeks out.” (Jeremiah 30:17) She has, as it is written “And a redeemer shall come to Zion…” (Isaiah 59:20) “And Sarai was barren; she had no child,” (Genesis 11:30) and she had, “And Sarah conceived and bore a son to Avraham…” (Genesis 21:2) And so too “…and Peninnah had children, but Hannah had no children,” (Shmuel I 1:2) and she had, “…and she conceived and bore three sons…” (Shmuel I 2:21) And so too, “Sing you barren woman who has not borne; burst out into song and jubilate, you who have not experienced birth pangs…” (Isaiah 54:1) and she had, as it says “And you shall say to yourself, "Who begot these for me…” (Isaiah 49:21)