According to several midrashic sources, a group from the tribe of Ephraim attempted to leave Egypt 30 years before the actual Exodus25. Here are the key points about this event:

1. Miscalculation of the exile: The Ephraimites miscalculated the duration of the Egyptian exile. They believed the 400 years mentioned in the Covenant Between the Parts (Genesis 15:13) began from the time of the prophecy itself, rather than from Isaac's birth 30 years later25.

2. Premature escape: Based on this miscalculation, a group of 300,000 Ephraimites attempted to leave Egypt 30 years before the actual time of redemption5.

3. Tragic outcome: The Ephraimites who left early were killed by the Philistines in the land of Gath23. This event is alluded to in 1 Chronicles 7:20-22, which describes the death of Ephraim's sons3.

4. Reason for the coastal route: The Midrash interprets Exodus 13:17 as referring to this recent tragedy. God did not lead the Israelites through Philistine territory during the actual Exodus to avoid reminding them of the Ephraimites' fate and discouraging them3.

5. Spiritual interpretation: Some commentators view this event as a prefiguration of the role of Mashiach ben Yosef (from the tribe of Ephraim) who will precede Mashiach ben David in the final redemption27.

6. Lesson learned: This incident serves as a cautionary tale against trying to force the redemption before its proper time and emphasizes the importance of unity among the Jewish people28.

It's important to note that this account is based on midrashic interpretations and is not explicitly mentioned in the biblical text. The story serves to explain certain biblical passages and convey moral and spiritual lessons.