Babylonian Talmud, Ta'anit 22a

Rabbi Beroka Hoza'ah used to spend time in the market at Bet Lapat where Elijah often appeared to him. Once he asked him, "Is there anyone in this market who has a share in the world to come?" He replied, "No." Meanwhile, he caught sight of a man wearing black shoes and who had no thread of blue on the corners of his garment and he exclaimed, "This man has a share in the world to come." Rabbi Beroka ran after him and asked him, "What do you do?" The man replied, "Go away and come back tomorrow." The next day he asked him again, "What do you do?" He replied, "I am a jailer and I keep the men and women separate and I place my bed between them so that they may not come to sin; when I see a Jewish girl upon whom the Gentiles cast their eyes I risk my life and save her. Once there was amongst us a betrothed girl upon whom the Gentiles cast their eyes. I therefore took sediment of red wine and put them on her skirt and I told them that she was menstruating." Rabbi Beroka asked the man, "Why have you no fringes and why do you wear black shoes?" He replied, "That the Gentiles amongst whom I constantly move may not know that I am a Jew, so that when a harsh decree is made against Jews I inform the rabbis and they pray to God and the decree is annulled." He further asked him, "When I asked you what you did why did you say to me, 'Go away now and come back tomorrow?'" He answered, "They had just issued a harsh decree and I said I would first go and acquaint the rabbis of it so that they might pray to God." While they were talking, two men passed by and Elijah remarked, "These two have a share in the world to come." Rabbi Beroka then approached and asked them, What do you do?" They replied, We are jesters, when we see men depressed we cheer them up; furthermore when we see two people quarreling we strive hard to make peace between them. [AJWS translation]