Matthew 5:37
34 But I say to you, do not take oaths at all—not by heaven, because it is the throne of God, 35 not by earth because it is his footstool, and not by Jerusalem, because it is the city of the great King. 36 Do not take an oath by your head because you are not able to make one hair white or black. 37 Let your word be ‘Yes, yes’ or ‘No, no.’ More than this is from the evil one. 38 “You have heard that it was said, ‘An eye for an eye and a tooth for a tooth.’ 39 But I say to you, do not resist the evildoer. But whoever strikes you on the right cheek, turn the other to him as well.
Ruth Rabbah 7
Aggadah“She said: Sit, my daughter, until you know how the matter will develop, as the man will not rest unless he finishes the matter today” (Ruth 3:18). “She said: Sit, my daughter.” Rabbi Huna [said] in the name of Rabbi Shmuel bar Rav Yitzḥak: The righteous, their 'yes' is yes and their 'no' is no, as it is stated: “As the man will not rest unless he finishes the matter today.”
Notes and References
"... In Rabbinic literature, as well, the words 'yes, yes' and 'no, no' are taken to imply an oath. Thus in tractate Shavuot, Raba explains that 'yes' alone is not an oath: 'But that is on condition that he said no, no twice or yes, yes twice ... and, then, since 'no' has to be said twice to mean an oath, so, too, yes must be said twice to mean an oath' ..."
Welborn, L. L. Politics and Rhetoric in the Corinthian Epistles (pp. 164-165) Mercer University Press, 1997