Commentary for Kiddushin 82:7

חדא מחדא לא אתיא תיתי חדא מתרתי הי תיתי

Now, let the Divine Law write [the principle of agency] in respect to sacrifices, and these others can come and be derived from them? - Because it may be refuted: as for sacrifice, that is because most of their operations are through an agent.<span class="x" onmousemove="('comment',' From the receiving of the blood onward, everything in connection with sacrifices was performed by priests acting on behalf of the Israelites who offered them.');">¹⁵</span> One cannot be derived from another: but let one be derived from two [others]?<span class="x" onmousemove="('comment',' By shewing that the factor common to both is also present in the third.');">¹⁶</span> - Which can be thus derived?

Daf Shevui to Kiddushin