Joshua 5:4-6

When the people of Israel left Egypt, all the males were already circumcised. However, during the forty years the people spent crossing the desert, none of the baby boys had been circumcised. Also, by the end of that time all the men who were of fighting age when they left Egypt had died because they had disobeyed the LORD. Just as he had sworn, they were not allowed to see the rich and fertile land that he had promised their ancestors.