שופטים ב:יז מדרש: Ruth Rabbah

“It was in the days when the judges judged, there was a famine in the land. A man of Bethlehem of Judah went to reside in the fields of Moav; he, his wife, and his two sons” (Ruth 1:1).
“It was in the days when the judges judged [shefot hashofetim].” Woe to the generation that judged their judges, and woe to the generation whose judges require judgment, as it is stated: “They also did not heed their judges” (Judges 2:17). Who were they [those judges]? Rav said: They were Barak and Deborah. Rabbi Yehosha ben Levi said: They were Shamgar and Ehud. Rav Huna said: They were Deborah, Barak, and Yael. Shefot – one, shofetim – two, hashofetim – three.