2 Samuel 21:6
Let seven men of his sons be delivered unto us, and we will hang them up unto the LORD in Gibeah of Saul, whom the LORD did choose. And the king said, I will give them. Let seven men of his sons be delivered unto us, and we will hang them up unto the LORD in Gibeah of Saul, whom the LORD did choose. And the king said, I will give them.
The treaty Joshua made with the Gibeonites remained binding upon Israel and carried consequences that lasted across generations. Because of that covenant the people were unable to fully drive out the heathen as God had intended. Although the treaty was a serious mistake with far-reaching effects, the Lord did not remove Joshua from his position as leader. In David's time the Gibeonites still possessed political rights, so that they could make an agreement with Israel's king and present their request to him.
Although they served as public servants, they were not chattel slaves but remained personally free, possessing their own homes, lands, families, and community. They asked David for seven of Saul's sons to be delivered to them, and David agreed to give them. Those men were hanged before the Lord at Gibeah of Saul. Their demand sought scriptural justice rather than revenge.
The account reflects the principle that an injury to one person was treated as an injury to the whole family, whose members were bound to help secure redress, just as one individual's offense could be charged to the family. It is a difficult account showing that God holds His people collectively responsible when the many allow the sins of the few to continue. It stands as an example of God's opposition to oppression and His refusal to tolerate it even when inflicted on people outside the household of faith. It falls within the later history that shows Nathan's prophetic denunciation being fulfilled through the judgments that came upon David.