וּכְתַבְתָּ֛ם עַל־מְזוּזֹ֥ת בֵּיתֶ֖ךָ וּבִשְׁעָרֶֽיךָ׃ (ס)
И напиши их на дверных столбах дома твоего и на воротах твоих.
Rashi on Deuteronomy
מזזות ביתך THE DOORPOSTS OF THY HOUSE — The word is written מזזת, to indicate that it is necessary to fix only one מזוזה to a door (cf. Menachot 34a).
Saadia Gaon on Deuteronomy
מזזות ביתיך ובשעריך, mezzuzot both inside your houses and your gates (courtyards.)