Y'hoshua (Jos) 5:6

because the people of Isra’el walked forty years in the desert until the whole nation, that is, the fighting men who had left Egypt, had died out; because they had not heeded what ADONAI said. ADONAI had sworn that he would not allow them to see the land which ADONAI swore to their ancestors that he would give us, a land flowing with milk and honey.