Exodus 27:20-21

“Command the people of Israel to bring you pure oil of pressed olives for the light, to keep the lamps burning continually. The lampstand will stand in the Tabernacle, in front of the inner curtain that shields the Ark of the Covenant. Aaron and his sons must keep the lamps burning in the LORD’s presence all night. This is a permanent law for the people of Israel, and it must be observed from generation to generation.