Positive commandment · Mitzvat Aseh #131 of 613
To give thanks, [reciting] the declaration concerning the tithes
להתוודות וידוי מעשר
The verse · Devarim 26:13
וְאָמַרְתָּ לִפְנֵי ה׳ אֱלֹהֶיךָ בִּעַרְתִּי הַקֹּדֶשׁ מִן־הַבַּיִת וְגַם נְתַתִּיו לַלֵּוִי וְלַגֵּר לַיָּתוֹם וְלָאַלְמָנָה כְּכׇל־מִצְוָתְךָ אֲשֶׁר צִוִּיתָנִי לֹא־עָבַרְתִּי מִמִּצְוֺתֶיךָ וְלֹא שָׁכָחְתִּי
“then thou shalt say before the Lord thy God, I have removed the hallowed things out of my house, and also have given them to the Levite, and to the stranger, to the fatherless, and to the widow, according to all thy commandments which thou hast commanded me: I have not transgressed thy commandments, neither have I forgotten them:”
The Rambam’s words
To give thanks, [reciting] the declaration concerning the tithes, as [Deuteronomy 26:13] states: "And you shall declare before G-d, your Lord, `I have removed the sacred [foods]...."'
להתוודות וידוי מעשר, שנאמר: "ואמרת לפני ה' אלוהיך ביערתי הקודש" (דברים כו,יג).
Why · Sefer HaChinuch #607
Declaration of tithes
“It is from the root of the commandment [that it is] since the uniqueness of man and his great praise is his speech, such that with it, he exceeds all the types of creatures.”
Who & when
“And this commandment is practiced at the time of the [Temple] by males.”
Where in the Mishneh Torah
Hilchot Second Tithes and Fourth Year's Fruit הלכות מעשר שני ונטע רבעי