Exodus 8:2
"And if thou refuse to let them go, behold, I will smite all thy borders with frogs:"
Cross References (ranked by relevance)
Exodus 7:14
And the LORD said unto Moses, Pharaoh’s heart is hardened, he refuseth to let the people go.
Psalm 78:45
He sent divers sorts of flies among them, which devoured them; and frogs, which destroyed them.
Exodus 9:2
For if thou refuse to let them go, and wilt hold them still,
Psalm 105:30
Their land brought forth frogs in abundance, in the chambers of their kings.