Numbers 18:11

18:11 “And this is yours: the raised offering of their gift, along with all the wave offerings of the Israelites. I have given them to you and to your sons and daughters with you as a perpetual ordinance. Everyone who is ceremonially clean in your household may eat of it.

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 ¹  from it as a raised offering to the Lord a tenth of the tithe.

[18:26]  ¹ tn The verb in this clause is the Hiphil perfect with a vav (ו) consecutive; it has the same force as an imperfect of instruction: “when…then you are to offer up.”