Shemot 27:20-21

And thou shalt command the Bnei Yisroel, that they bring thee pure pressed shemen zayit (olive oil) for the ohr, to kindle the Ner Tamid (Perpetual Lamp). In the Ohel Moed outside the Parochet, which is before the Edut, Aharon and his banim shall arrange it from erev to boker before HASHEM; it shall be a chukkat olam unto their dorot from the Bnei Yisroel.