According to Jewish sources, 300,000 Ephraimites were killed in a failed attempt to leave Egypt early before the actual Exodus12.

This tradition comes from a midrash that explains why God did not lead the Israelites on a direct route to Canaan after leaving Egypt. The midrash states that God avoided taking them through Philistine territory because they would have seen "the bones of 300,000 Israelites from the tribe of Ephraim, laying in heaps on the road"4.

The story goes that some Ephraimites miscalculated the end of the 400 years of slavery prophesied to Abraham and left Egypt 30 years too early on their own. They were then slaughtered by the Philistines4.

This midrash serves to explain the verse in Exodus 13:17 about God not leading the Israelites by way of the land of the Philistines. It suggests God wanted to spare the newly freed Israelites from seeing this horrific sight of their brethren's bones, which might have made them want to return to Egypt4.

While the specific number of 300,000 is not found in earlier biblical texts, it emerges in later rabbinic literature as an explanation for God's chosen route out of Egypt. The midrash uses this dramatic story to underscore themes of divine wisdom and the dangers of trying to force the prophesied redemption before its proper time.