Numbers 5:13

13 so that another man has sexual relations with her, and this is hidden from her husband and her impurity is undetected (since there is no witness against her and she has not been caught in the act),

Read Numbers 5:13 Using Other Translations

And a man lie with her carnally, and it be hid from the eyes of her husband, and be kept close, and she be defiled, and there be no witness against her, neither she be taken with the manner;
if a man lies with her sexually, and it is hidden from the eyes of her husband, and she is undetected though she has defiled herself, and there is no witness against her, since she was not taken in the act,
and has sex with another man, but neither her husband nor anyone else knows about it. She has defiled herself, even though there was no witness and she was not caught in the act.