Deuteronomy 14:27

והלוי … לא תעזבנו AND THE LEVITE [THAT IS WITHIN THY GATES;] THOU SHALT NOT FORSAKE HIM by not giving him the “First Tithe” (מעשר ראשון). כי אין לו חלק ונחלה עמך OR HE HATH NO PORTION NOR INHERITANCE WITH THEE — This excludes “Gleanings” (לקט), “the forgotten sheaf” (שכחה), the “corner of the field” (פאה), and ownerless things (הפקר) from the things that must be tithed — for he (the Levite) has a portion in them (is entitled to take of them) with you, just the same as you, and they are therefore exempt from tithes (Mishnah Challah 1:3; Bava Kamma 94a).

וְהַלֵּוִ֥י אֲשֶׁר־בִּשְׁעָרֶ֖יךָ לֹ֣א תַֽעַזְבֶ֑נּוּ כִּ֣י אֵ֥ין ל֛וֹ חֵ֥לֶק וְנַחֲלָ֖ה עִמָּֽךְ׃ {ס}        

and the Levite who is within thy gates; thou shalt not forsake him; for he has no part or inheritance with thee.