Leviticus 5:1, 4

‘If a person sins in hearing the utterance of an oath, and is a witness, whether he has seen or known of the matter—if he does not tell it, he bears guilt.

‘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.