Two women lived as close friends in one of the towns of late antique Israel. One day one of them was kneading dough at her neighbor's house, and a gold dinar slipped out of her purse, fell into the dough, and was silently absorbed into the lump. She did not notice, and she went home.
Later she discovered the coin was missing and came back to ask. Did you find my dinar? The neighbor had not noticed the coin and answered honestly that she had not. But then she went further than the question demanded. I swear by the life of my husband and by the lives of my two children that I do not have it. In biblical Hebrew idiom, swearing on a life is binding what one loves most to the truth of one's words. It is a terrible oath to swear lightly.
Within a short span of time, her husband died. Both of her children died. The village came to sit shiva with her. A meal of consolation was prepared. The bread was broken at the mourner's table, and there, inside the loaf baked with that dough, the missing dinar rolled out.
This exemplum, preserved as number 121b in Moses Gaster's 1924 Exempla of the Rabbis, is one of the sharpest mussar tales in the whole collection. The neighbor had not stolen. She had not even lied about the coin knowingly. Her crime was swearing an oath that she did not need to swear. The Torah says, You shall not take the name of the Lord your God in vain (Exodus 20:7). Our sages understood this to include swearing on what is precious when a simple no would have done. The coin was found. Everything else was lost. Oaths are made of fire; they consume what they touch.