R. Yudan was a teacher and judge who lived in the fourth century in Tiberias, where he studied under Rabbi Abba. Though he appears freqently in the Talmud Yerushalmi and in the Midrash, almost nothing is known about his life or his family. Most of what is recorded from him is in the area of aggadah (non-legal teachings, including biblical interpretation and parables).
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Rebbi Simeon ben Laqish was thinking very hard about Torah. He overstepped the Sabbath boundary without noticing it, to confirm (Prov. 5:19): “In its love you will always err.” Rebbi Yudan ben Rebbi Ismael was thinking very hard about Torah. His toga slipped off from him and he did not notice it, to confirm: “In its love you will always err.” Rebbi Eleazar ben Rebbi Simeon was thinking very hard about Torah. His toga slipped off from him but a viper was caring for it…