One Joseph, a Jew, who honored the Sabbath, had a very rich neighbor, who was a firm believer in astrology. He was told by one of the professional astrologers that his wealth would become Joseph's. He therefore sold his estate, and bought with the proceeds a large diamond, which he sewed in his turban, saying, " Joseph can never obtain this. It so happened, however, that while standing one day upon the deck of a ship in which he was crossing the sea, a heavy wind arose and carried the turban from his head. A fish swallowed the diamond, and being caught and exposed for sale in the market, was purchased by Joseph to supply his table on the Sabbath eve. Of course, upon opening it he discovered the diamond.
Joseph the Sabbath-Keeper and the Diamond in the Fish
Hebraic Literature (1901), Midrashim — cf. Shabbat 119a