It is possible to explain the phrase "When Pharaoh sent" in another way, based on the Midrash brought by the Parashat Derakhim (Derekh Mitzrayim Derush 5), "Moshe said to Pharaoh, we will not leave here until you say, 'You are on your own, you are free people'." Thus, it can be said that because of this statement that Moshe forced Pharaoh to say, it is said "When Pharaoh sent," referring to this sending with his verbal declaration, where he said, "You are on your own, you are free people."

Now, the essence of this Midrash requires an explanation: why and for what purpose did Moshe need this statement from Pharaoh, since if Pharaoh was not obstructing the Israelites' departure, they could have left even without his explicit consent. The Parashat Derakhim explains that there is a practical difference regarding the law of granting gifts; one who frees his slave is not permitted to send him away empty-handed but is obligated to give him gifts: "you shall furnish him liberally from your flock, from your threshing floor, and from your wine press" (Deuteronomy 15:13-14). However, this law only applies to a slave who is released by the master according to the law, as it is stated (ibid.), "And when you send him away." But a runaway slave is not entitled to such gifts (Rambam, Hilchot Avadim 3:15).

From now on, says the Parashat Derakhim, we can say that this Midrash holds that what the Israelites took from Egypt - silver and gold vessels - was in accordance with the law of granting gifts. If they had left without Pharaoh's permission, they would not have been entitled to the spoils of Egypt, as they would be like a runaway slave who does not receive gifts. Therefore, Moshe Rabbeinu, of blessed memory, had to compel Pharaoh to say, "You are on your own, you are free people," so that they would be entitled to the spoils of Egypt according to the law of granting gifts. This is the end of the explanation.