Reference for Bava Kamma 63:20

ממאי מדקתני או שהיו שניהם רצין פטורין הא תו ל"ל השתא אחד רץ ואחד מהלך פטור שניהם רצין מבעיא אלא הכי קאמר אחד רץ ואחד מהלך פטור בד"א בע"ש בין השמשות אבל בחול אחד רץ ואחד מהלך חייב שניהם רצין אפי' בחול פטורין

[The Mishnaic text however] not only fails to be of any support [in this respect], but affords a contradiction to Resh Lakish, [in whose view] the reason [even for the liability] is that the lying cow kicked the walking cow, thus [implying] that [the latter] sustained damage [because of the former cow] through sheer accident, and there would be exemption. Now, [the case of] the Mishnah surely deals with accidental damage, and still states liability? — The Mishnah [deals with a case] where the beam blocked the [whole] passage as if by a carcass,<span class="x" onmousemove="('comment',' Consequently the liability extends even to accidental damage. ');">¹⁶</span>

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