Nedarim 45a נדרים מ״ה א

If you wish, say instead: That baraita, in which it is taught that the item does not leave the possession of the owner until it enters the possession of another, is referring to a case where one declared it ownerless before two people; and this baraita, in which it is taught that the item is ownerless when it is declared ownerless, is referring to a case where one declared it ownerless before three people. As Rabbi Yoḥanan said in the name of Rabbi Shimon ben Yehotzadak: With regard to anyone who declares an item ownerless before three people, that item is ownerless; if he does so before two people, it is not ownerless.

And Rabbi Yehoshua ben Levi said: By Torah law, even with one person, the item is ownerless, and what is the reason that the Sages said that ownerless status must be declared with three people? It is so that one will take possession of the item and two will testify that the item was declared ownerless and that it was acquired by that person. It is not a requirement fundamental to the declaration of ownerless status.