They tell the story about Shmuel’s father, that people used to deposit orphans’ money in his place as a trust.

Why there? Because Shmuel’s father used to hide that money in the inner space of a millstone.

One sunny day Shmuel asked his father: “Father, father, where do you hide the orphans’ money?”

And the father answered: “In the inner space of the millstone: the upper and the lower money bundles are ours, and the middle ones belongs to the orphans, so that if the money will be stolen, it will be stolen from us, and if the ground will get wet, our money will get wet, and the orphans’ money will be safe.”

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source: Talmud, Blessing Gate, page 18: