Exodus 27:20-21

20“Also you are to command Bnei-Yisrael, that they are to bring to you pure olive oil beaten for the light, to cause a lamp to burn continually.

21In the Tent of Meeting, outside the curtain which is before the Testimony, Aaron and his sons will set it in order, to burn from evening to morning before Adonai. It will be a statute forever throughout their generations, on behalf of Bnei-Yisrael.