The Midrash that discusses the tribe of Ephraim leaving Egypt prematurely is found in Midrash Rabbah on Exodus (Shemot Rabbah) 20:11. This Midrash elaborates on Exodus 13:17, which states that God did not lead the Israelites through the land of the Philistines when they left Egypt13.

According to this Midrash:

1. The Ephraimites miscalculated the end of the 400-year period of slavery that God had foretold to Abraham.

2. They left Egypt 30 years before the divinely ordained time of the Exodus.

3. Approximately 200,000-300,000 Ephraimites departed prematurely.

4. They traveled through the land of the Philistines and were killed in battle at Gath134.

The Midrash explains that this tragic event is why God chose not to lead the Israelites through Philistine territory during the actual Exodus. He wanted to avoid having the people see the bones of their brethren, which might have discouraged them and caused them to return to Egypt13.

This story is also referenced in other rabbinic sources:

1. The Babylonian Talmud (Sanhedrin 92b) mentions this event when discussing the dry bones that Ezekiel resurrected in his vision.

2. Targum Yonatan, an Aramaic translation and interpretation of the Hebrew Bible, also cites this story in its commentary on Exodus 13:173.

This Midrashic tradition serves to explain several biblical passages and emphasizes the importance of waiting for divine timing rather than acting on human calculations alone14.