Leviticus 5:4-5

4‘Or if a person swears, speaking thoughtlessly with his lips to do evil or to do good, whatever it is that a man may pronounce by an oath, and he is unaware of it—when he realizes it, then he shall be guilty in any of these matters.

5‘And it shall be, when he is guilty in any of these matters, that he shall confess that he has sinned in that thing;