The Lord did as Moses asked.

The LORD then spoke to Moses: Speak to Aaron: Stretch out your hand with your staff over the streams, the canals, and the ponds, and make frogs overrun the land of Egypt.  So Aaron stretched out his hand over the waters of Egypt, and the frogs came up and covered the land of Egypt.

Then Pharaoh summoned Moses and Aaron and said, “Pray to the LORD to remove the frogs from me and my people, and I will let the people go to sacrifice to the LORD.” 

After Moses and Aaron left Pharaoh’s presence, Moses cried out to the LORD on account of the frogs that he had inflicted on Pharaoh; and the LORD did as Moses had asked.

Exodus 8: 1-2, 4, 8-9