וְאֶל־הַלְוִיִּ֣ם תְּדַבֵּר֮ וְאָמַרְתָּ֣ אֲלֵהֶם֒ כִּֽי־תִ֠קְחוּ מֵאֵ֨ת בְּנֵֽי־יִשְׂרָאֵ֜ל אֶת־הַֽמַּעֲשֵׂ֗ר אֲשֶׁ֨ר נָתַ֧תִּי לָכֶ֛ם מֵאִתָּ֖ם בְּנַחֲלַתְכֶ֑ם וַהֲרֵמֹתֶ֤ם מִמֶּ֙נּוּ֙ תְּרוּמַ֣ת יְהוָ֔ה מַעֲשֵׂ֖ר מִן־הַֽמַּעֲשֵֽׂר׃
"Parle aussi aux Lévites et dis-leur: Lorsque vous aurez reçu des enfants d’Israël la dîme que je vous donne de leur part, pour votre héritage, vous prélèverez là-dessus, comme impôt de l’Éternel, la dîme de la dîme.
Mishneh Torah, Gifts to the Poor
As for ma'asér rishon that was taken for the Levite, he [the Levite] separates from it one-tenth and gives it to a priest. It is called terumat ma'aser [the "gift offering of the tithe"], and about this it is written, (Num. 18:26) Speak to the Levites [and say to them: When you receive from the Israelites their tithes, which I have assigned to you as your share, you shall set aside from them one-tenth of the tithe as a gift to the LORD].
Mishneh Torah, Leavened and Unleavened Bread
One does not fulfill his obligation by eating matsa that is forbidden to him, such as if he ate it untithed, or [as] first tithe from which the priestly tithe was not taken or if he stole it. This is the general principle: We fulfill our obligation with anything upon which we may recite the Grace after the Meals. And we do not fulfill our obligation with anything upon which we may not recite the Grace after the Meals.
Mishneh Torah, Positive Mitzvot
To set apart the tithe of the corn for the Levites, as it is said, “And all the tithe of the land, whether of the seed of the land or of the fruit of the tree, (is the Lord’s)” (Lev. 27:30).