וְשָׁכַ֨ב אִ֣ישׁ אֹתָהּ֮ שִׁכְבַת־זֶרַע֒ וְנֶעְלַם֙ מֵעֵינֵ֣י אִישָׁ֔הּ וְנִסְתְּרָ֖ה וְהִ֣יא נִטְמָ֑אָה וְעֵד֙ אֵ֣ין בָּ֔הּ וְהִ֖וא לֹ֥א נִתְפָּֽשָׂה׃
and a man lie with her carnally, and it be hid from the eyes of her husband, she being defiled secretly, and there be no witness against her, neither she be taken in the act;
Rashi on Numbers
ושכב איש AND A MAN LIETH [WITH HER] — a man, thus excluding a minor and a being that does not come under the term איש (i. e., an animal) (Sifrei Bamidbar 7:2; Sotah 24a).
Sforno on Numbers
ושכב איש אותה, and another man has lain with her It is characteristic of the evil urge to cause the sinner to proceed from a relatively mild sin to ever more serious sins.
Rashbam on Numbers
ועד אין בה, to testify that she had been guilty of adultery,