Rabbi Yohanan persuaded Rabbi Shimon ben Lakish, also known as Reish Lakish, to study Torah. He taught him himself until Reish Lakish became a great scholar and a close friend. A halakhic dispute between them developed into an exchange of mutual insult and offense, and ultimately both of their lives ended in tragic circumstances.

One day Rabbi Yohanan was swimming in the Jordan River. Reish Lakish saw him and jumped after him into the Jordan. Rabbi Yohanan said to Reish Lakish: Your strength would be ideally used for Torah study. Reish Lakish said to him: Your beauty is fit for belonging to women. Rabbi Yohanan said to him: If you repent, I will give you my sister, who is more beautiful than I am, as a wife. Reish Lakish committed himself to study Torah. Then, Reish Lakish wanted to return to dry land and retrieve his garments, but was unable to return. Rabbi Yohanan taught Reish Lakish Bible and Mishna, and he rendered him a great man.

One day the Sages disagreed in the study hall: With regard to a sword, knife, dagger, spear, hand sickle, and a harvest sickle, from when are they susceptible to ritual impurity? From the time their manufacture is complete. When is their manufacture complete? Rabbi Yohanan said: From when one fires them in the furnace; Reish Lakish said: From when one scours them in cold water. Rabbi Yohanan said to Reish Lakish: A bandit knows his banditry.

Reish Lakish said to him: How have you benefited me by bringing me close to Torah? There, [when I was leader of the bandits], they called me master; here, too, they call me Master. Rabbi Yohanan said to him: I benefited you, as I brought you near, under the wings of the Divine Presence.

Rabbi Yohanan was offended. Reish Lakish fell ill [as a consequence of Rabbi Yohanan’s taking offense]. Rabbi Yohanan’s sister [who was married to Reish Lakish] came to Rabbi Yohanan and wept. She said to him: Act [pray for Reish Lakish] for the sake of my children, so they will not be orphaned. Rabbi Yohanan said to her: “Leave your orphans; I will sustain them” (Jeremiah 49:11). She said: Do so for the sake of my widowhood, so that I will not be widowed. He said to her: “And your widows should rely on Me” (Jeremiah 49:11). Rabbi Shimon ben Lakish passed away. Rabbi Yohanan was exceedingly upset over his passing.

The other Sages said: Who will go to settle Rabbi Yohanan’s mind in the wake of his loss? They said: Let Rabbi Elazar ben Pedat go, as his statements are sharp. [He will be an appropriate replacement for Reish Lakish.]…Rabbi Elazar ben Pedat went and sat before Rabbi Yohanan. Every matter that Rabbi Yohanan would say, Rabbi Elazar ben Pedat would reply to him: It is taught in a baraita in support of your opinion. Rabbi Yohanan said: Are you like ben Lakish? With ben Lakish, when I would state a matter, he would challenge me with twenty-four difficulties, and I would respond to him with twenty-four responses; consequently, the halakha would become clarified. But you say: It is taught in a baraita in support of your opinion; don’t I know that what I said is correct?

Rabbi Yohanan would go and rend his garments, weeping and saying: Where are you, ben Lakish? Where are you, ben Lakish? He screamed until he lost his mind and became insane. The Sages prayed for mercy for him to put an end to his suffering, and he died. (Bava Metzia 84a–b)