Rashi on Deuteronomy 4:28/רש"י על דברים ד׳:כ״ח

1ועבדתם שם אלהים AND THERE YE SHALL SERVE GODS — Understand this as the Targum does: And there ye shall serve peoples who serve idols, for since you serve those who serve them (idols) it will be as though you serve them.