Reference for Bava Metzia 57:1

אלא כשנשתמש בהן אבל לא נשתמש בהן אם אבדו פטור

[apparently] only if he [the finder] did use it. But if not, [all would agree] that if it is lost he is free [from responsibility]. Shall we say that this refutes R. Joseph? For it has been stated. A bailee of lost property: Rabbah ruled, he ranks as an unpaid bailee; R. Joseph maintained. as a paid bailee!<span class="x" onmousemove="('comment',' And since a paid bailee is liable for loss, our Mishnah appears to refute R. Joseph. ');">¹</span>

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