For the source text click/tap here: Bava Kamma 104
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Rav Yehudah in the name of Shmuel says (104a) that one may not give over money on the basis of a Deyukni even if witnesses are signed on it.
RASHI (DH b'Deyukni) explains that a person deposited his money with a Shomer (guardian) and now wishes to appoint a Shali'ach (agent) to retrieve the object. He gives the Shali'ach identifying signs which the agent uses to prove that he is acting on behalf of the owner of the money.
Rebbi Yochanan disagrees with Shmuel and maintains that if witnesses sign the document, the Shomer may rely on the Deyukni.
Rashi (and most of the other commentaries, as well) understand the Gemara’s discussion to be a debate about establishing agents in general, although the Bartenura suggests that it is limited to the case of our Mishna and discusses only returning stolen objects.
In light of the recent discussions of Takanat Hashavim I thought we might explore the Sin of King David in rabbinic literature.