Reference for Zevachim 169:9
לא הא שחוטין מהן ירדו מהן לא ירדו והא כולן קתני כולם אחיין
That is obvious?<span class="x" onmousemove="('comment',' Obviously they cannot remain there but must be brought down and slaughtered, and then they will be taken up again. If then this is not taught for the sake of the inference (viz., that all of these, if slaughtered, do not descend) , it is altogether superfluous.');"><sup>8</sup></span> - In truth it refers to living animals which have a cataract in the eye, this being in accordance with R'Akiba who maintained that if these ascend they do not descend.<span class="x" onmousemove="('comment',' V. supra 77b. The Mishnah thus informs us that they must descend, and even if subsequently slaughtered they may not re-ascend.');"><sup>9</sup></span>