This reference to the time when the plague should be removed at Pharaoh's own appointment, prevented the possibility of having it supposed that it was the effect of human contrivance, and made it a more full demonstration of a divine power. Deuteronomy 32:35.
Related Commentaries of Exodus 8:9
Exodus 8:9-10
9 And Moses said unto Pharaoh, Gloryb over me: when shall I intreat for thee, and for thy servants, and for thy people, to destroy the frogs from thee and thy houses, that they may remain in the river only?
10 And he said, To morrow.c And he said, Be it according to thy word: that thou mayest know that there is none like unto the LORD our God.