Mishna, Pirkei Avot 5:9

Wild beasts come upon the world because of false oaths, and for the desecration of the Divine Name. Exile comes upon the world because of idolaters, for incest, for bloodshed, and because of (neglect of) the (Sabbatical) release of the land. Pestilence increases at four periods: In the fourth year; in the seventh year; in the year after the seventh year; and at the conclusion of the Feast each year. In the fourth year, because of the Poor man's Tithes in the third year; in the seventh year, because of the Poor man's Tithes in the sixth year; in the year after the seventh year, because of the seventh year produce; and at the end of the Feast each year, for robbing the gifts of the poor. [Moreshet translation]