מִקְצֵ֣ה ׀ שָׁלֹ֣שׁ שָׁנִ֗ים תּוֹצִיא֙ אֶת־כָּל־מַעְשַׂר֙ תְּבוּאָ֣תְךָ֔ בַּשָּׁנָ֖ה הַהִ֑וא וְהִנַּחְתָּ֖ בִּשְׁעָרֶֽיךָ׃
At the end of every three years, even in the same year, thou shalt bring forth all the tithe of thine increase, and shall lay it up within thy gates.
Sifrei Devarim
(Devarim 14:28) "(If one delayed giving his tithes of the first and second years) From the end of three years, you shall remove all the tithe of your produce": I might think, even on the festival; it is, therefore, written (Ibid. 26:12) "When you finish tithing" (and the tithing of the third year's produce is not completed until Channukah of the fourth year).