Joshua 5:3 (KJV)

And it came to pass, when all the kings of the Amorites, which were on the side of Jordan westward, and all the kings of the Canaanites, which were by the sea, heard that the Lord had dried up the waters of Jordan from before the children of Israel, until we were passed over, that their heart melted, neither was there spirit in them any more, because of the children of Israel.

At that time the Lord said unto Joshua, Make thee sharp knives, and circumcise again the children of Israel the second time.

And Joshua made him sharp knives, and circumcised the children of Israel at the hill of the foreskins.

And this is the cause why Joshua did circumcise: All the people that came out of Egypt, that were males, even all the men of war, died in the wilderness by the way, after they came out of Egypt.

Now all the people that came out were circumcised: but all the people that were born in the wilderness by the way as they came forth out of Egypt, them they had not circumcised.