Numbers 5:15

5:15 then the man must bring his wife to the priest, and he must bring the offering required for her, one tenth of an ephah of barley meal; he must not pour olive oil on it or put frankincense on it, because it is a grain offering of suspicion, a grain offering for remembering, for bringing iniquity to remembrance.

Numbers 18:26

18:26 “You are to speak to the Levites, and you must tell them, ‘When you receive from the Israelites the tithe that I have given you from them as your inheritance, then you are to offer up from it as a raised offering to the Lord a tenth of the tithe.