'Took an Oath' in the Bible

Saul accepted Jonathan's advice and took an oath, "As surely as the Lord lives, he will not be put to death."

Then David {took an oath} again and said, "Your father knows very well that I have found favor in your eyes, and he thought, 'Do not let Jonathan know this, lest he worry.' But {as Yahweh lives} and {as your soul lives}, surely [there is] merely a step between me and death!"

And Jonathan again took an oath to David, because of his love for him: for David was as dear to him as his very soul.