Joshua 5:8

‘And so it was that when they had finished circumcising all the nation, they stayed in their places in the camp until they were whole.'

Having undergone the rite of circumcision all the males under forty were in some discomfort and had to rest up in the camp. It has been questioned whether a general would have carried out such an operation on his troops in such a situation, but he knew that the people of Jericho were afraid and remaining in their city, that there was no evidence of any other troop movement through the hills, and that YHWH had just revealed His power by the crossing of the Jordan. Thus such a necessary operation in order to celebrate the first Passover in the land was quite reasonable in such a situation.