Numbers 15:21
You must give to the Lord some of the first of your finely ground flour as a raised offering in your future generations.
Exodus 29:28
It is to belong to Aaron and to his sons from the Israelites, by a perpetual ordinance, for it is a contribution. It is to be a contribution from the Israelites from their peace offerings, their contribution to the Lord.
Numbers 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.