Musannaf Ibn Abi Shayba 27:202

Shababa narrated to us, from Yunus ibn Abi Ishaq, from Abu Ishaq, from Amr ibn Maymun, from Abdullah ibn Mas’ud: That when Moses, peace be upon him, took the Children of Israel by night, it reached Pharaoh. So he ordered a sheep, and it was slaughtered. Then he said, "No, by Allah, it will not be finished being skinned until six hundred thousand of the Copts have gathered to me." He said: So Moses, peace be upon him, set out until he reached the sea. He said to it, "Split!" The sea said, "You have asked for much, O Moses! Has it ever split for anyone from the children of Adam so that it would split for you?" He said: And with Moses, peace be upon him, was a man on a horse. That man said to him, "Where have you been commanded [to go], O Prophet of Allah?" He said, "I have not been commanded except in this direction." He said, so he urged his horse forward, and it swam with him, then he came out. He said, "Where have you been commanded [to go], O Prophet of Allah?" He said, "I have not been commanded except in this direction." He said, "By Allah, you have not lied, nor have you been lied to." He said: Then he urged it forward a second time, and it swam with him, then he came out. He said, "Where have you been commanded [to go], O Prophet of Allah?" He said, "I have not been commanded except in this direction." He said, "By Allah, you have not lied, nor have you been lied to. By Allah, you have not lied, nor have you been lied to." He said: Then Allah revealed to Moses, peace be upon him, "Strike with your staff." So Moses struck with his staff, and it split. Every part was like a great fortress, like a great mountain. There were twelve paths in it for the twelve tribes, for each tribe a path, [where] they could see one another. When the companions of Moses, peace be upon him, had exited, and the companions of Pharaoh had completed [their entry], the sea met upon them and drowned them.