Reference for Bava Kamma 70:18

גופא אמר רבה בר נתן טענו חטין והודה לו בשעורין פטור מאי קמ"ל תנינא טענו חטין והודה לו בשעורין פטור

that the Mishnah thought fit to let us know that this view ought not to be accepted? — [Hence it must be said:] No; but that the concluding clause [deals with a case where] the plaintiff was doubtful and the defendant certain, and the opening clause<span class="x" onmousemove="('comment',' Where the defendant pleads that 'the pursued ox was injured by a rock…'. ');">¹³</span>

Jastrow