Where did the LORD swear that the old generation would not enter the land of promise?
Joshua 5:6 (ESV)
6For the people of Israel walked forty years in the wilderness, until all the nation, the men of war who came out of Egypt, perished, because they did not obey the voice of the LORD;the LORD swore to them that he would not let them see the land that the LORD had sworn to their fathers to give to us, a land flowing with milk and honey.
In Numbers 14:20–38 the Lord declared that the old generation would die in the wilderness and not enter into the land of Canaan.
6 For the people of Israel walked forty years in the wilderness, until all the nation, the men of war who came out of Egypt, perished, because they did not obey the voice of the LORD; the LORD swore to them that he would not let them see the land that the LORD had sworn to their fathers to give to us, a land flowing with milk and honey.