מדרש אויף תהילים 78:49

(Exodus 12:12) "And I shall pass ("ve'avarti") through the land of Egypt": R. Yehudah says: As a king, who makes the rounds of his kingdom. Variantly: I shall place My wrath ("evrathi") and My fear in Egypt. "evrah" is wrath, as in (Psalms 78:49) "He sent His burning anger upon them — evrah and scorn, and affliction," and (Isaiah 13:9) "Behold, the day of the L–rd is coming — fury and evrah and burning wrath, etc."

R. Eliezer says: Whence is it derived that every plague with which the Egyptians were smitten in Egypt was four-fold, etc.?

R. Akiva says: Whence is it derived that every plague with which the Egyptians were smitten in Egypt was five-fold? (Say, then, that in Egypt they were smitten with fifty) plagues, and at the sea with two hundred and fifty.