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.
Pirkei Avot
Wild beasts come to the world for swearing in vain, and for the profanation of the Name. Exile comes to the world for idolatry, for sexual sins and for bloodshed, and for [transgressing the commandment of] the [year of the] release of the land. At four times pestilence increases: in the fourth year, in the seventh year and at the conclusion of the seventh year, and at the conclusion of the Feast [of Tabernacles] in every year. In the fourth year, on account of the tithe of the poor which is due in the third year. In the seventh year, on account of the tithe of the poor which is due in the sixth year; At the conclusion of the seventh year, on account of the produce of the seventh year; And at the conclusion of the Feast [of Tabernacles] in every year, for robbing the gifts to the poor.