Midrash sur Rois 2 5:16

Abraham — (Bereshith 14:22-23) "I lift my hand (in oath) to the L-rd, G-d on high, Possessor of heaven and earth: Nothing (shall I take), from a thread until a sandal latchet, nor shall I take anything that is yours." Boaz (to Ruth) — (Ruth 3:13) (I swear) "As the L-rd lives, lie (here with me, unmolested) until the morning…" David — (I Samuel 26:10) "And David said (to Avishai, who wanted to kill Saul, David's enemy): (I swear) as the L-rd lives: The L-rd will strike him with plague, or his day will come and he will die, or he will go forth in battle and he will perish." Elisha — (II Kings 5:16) "(I swear) as the L-rd lives, before whom I have stood, I shall not take (any emolument, etc.") And just as the righteous beswear their (evil) inclination not to do (as it wishes), so, the wicked (beswear it to do) as it wishes, viz. (Ibid. 20) "As the L-rd lives, I (Gechazi, Elisha's servant) shall run after him and take something from him!"