Tazria 

תזריע

According to the Sages, the type of leprosy detailed in the Torah is a punishment for malicious speech. In this tale, a merchant offers passersby an elixir of life: Be scrupulous with your speech and your actions. 

“This shall be the law of the leper” (Leviticus 14:2) – that is the meaning of what is written: “Who is the man who desires life, loving his days to see good?” (Psalms 34:13). There was an incident involving a peddler circulating in the towns that were adjacent to Tzipori. He would proclaim: Let anyone who wishes to purchase an elixir of life come and take it. He entered Akhbera and approached the residence of Rabbi Yannai. Rabbi Yannai was sitting and changing clothes in his room, and heard him proclaim: Is there anyone who wishes to purchase an elixir of life? Rabbi Yannai said to him: Come and enter here, sell it to me. The peddler said to him: You and those like you do not need to get it [from me, as you already have it]. Rabbi Yannai implored him to enter, and he entered. The peddler took out a scroll of Psalms, and showed him this verse: “Who is the man who desires life, loving his days to see good?” (Psalms 34:13). What is written after it? “Guard your tongue from evil and your lips from speaking deceit. Turn away from evil and do good; seek peace and pursue it” (Psalms 34:14–15). Rabbi Yannai said: All my days I would read this verse, but I did not know how straightforward it is, until this peddler came and informed me: “Who is the man who desires life.” Therefore, Moses cautioned the Israelites and said to them: “This shall be the law of the leper [<source>(<i>Vayikra</i> <i>Rabba</i> 16)  </source>