Êxodo 14:15 Midrash: Mekhilta DeRabbi Yishmael, Ein Yaakov (Glick Edition), Pesikta Rabbati & Midrash Tanchuma

(Exodus 14:15) "And the L–rd said to Moses: Why do you cry out to Me?" R. Yehoshua says: The Holy One Blessed be He said to Moses: Moses, all that Israel has to do is to go forward.

R. Yehudah b. Betheirah says: The Holy One Blessed be He said to him: I have already fulfilled My promise to your father Abraham, viz. (Exodus, Ibid. 21) "and He made the sea into the dry land" (that He had promised to Abraham) (Ibid. 29) "and the children of Israel walked in the dry land (that had already been made) in the midst of the sea."

Rebbi says: Last night you said (i.e., you complained to Me) (Exodus 5:23) "And from the time I came to Pharaoh, etc." And now you stand and wax long in prayer? "Why do you cry out to Me?" Rebbi says (Exodus 14:15) "Speak to the children of Israel and have them go forward ('veyisa'u')." Have them retract ('yasiu') the things that they said. Last night they said (Ibid. 11) "Is it for lack of graves, etc.?" and now you stand and wax long in prayer (for them)? "Why do you cry out to Me?" Let them retract what they have said.