וּכְתַבְתָּ֛ם עַל־מְזוּזֹ֥ת בֵּיתֶ֖ךָ וּבִשְׁעָרֶֽיךָ׃ (ס)
또 네 집 문설주와 바깥 문에 기록할지니라
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.)