'Oath' in the Bible

Then they came to urge David to eat bread while it was still day, but David took an oath: “May God punish me and do so severely if I taste bread or anything else before sunset!”

So the king said to Shimei, “You will not die.” Then the king gave him his oath.

The Gibeonites were not Israelites but rather a remnant of the Amorites. The Israelites had taken an oath concerning them, but Saul had tried to kill them in his zeal for the Israelites and Judah. So David summoned the Gibeonites and spoke to them.

David spared Mephibosheth, the son of Saul’s son Jonathan, because of the oath of the Lord that was between David and Jonathan, Saul’s son.