Bava Metzia 74A

הכא לאו בידו.

By contrast, here, the matter is not in his power to determine whether or not to buy the wine, as perhaps the owner will not sell it to him.

אמר רבא: הני בי תלתא דיהבי זוזי לחד למזבן להו מידי וזבן לחד מינייהו ⁠– זבן לכולהו. ולא אמרן אלא דלא צר וחתים איניש איניש לחודיה. אבל צר וחתים איניש איניש לחודיה, למאן דזבן ⁠– זבן, ולמאן דלא זבן ⁠– לא זבן.

§ Rava said: In the case of these 3 people who gave money to one individual in order for him to purchase an item for them and he purchased the item for only one of them, he has actually purchased it for all of them. All 3 share ownership of that which was purchased, and the one for whom the item was purchased does not have any additional claim on the merchandise. And we said this ruling only when the agent did not wrap up and seal each person’s money separately but rather put all of the money in one bundle. But if he wrapped up and sealed each person’s money separately and spent the money of only one of them, he purchased the item only for the one for whom he purchased it, and he did not purchase the item for those for whom he did not purchase it.

אמר רב פפי משמיה דרבא: האי סיטומתא ⁠– קניא. למאי הלכתא? רב חביבא אמר: למקניא ממש.

Rav Pappi said in the name of Rava: In this case of labeling an item with a marker [situmta], which was commonly used to indicate that specific merchandise had been sold, even though the buyer had not yet paid and the item was still located in the seller’s warehouse, the labeling effects acquisition of the merchandise for the buyer. The Talmud asks: With regard to what halakha was this said? What is the significance of this acquisition? Rav Ḥaviva said: It means to actually effect acquisition, in other words, that the merchandise belongs to the buyer for all intents and purposes.