Musar for Shabbat 296:15

הכא במאי עסקינן בממנה אחרים עמו על פסחו דמעיקרא מיקדש וקאי

— Here it is different: since he is a habitue of his, it is as though he had enrolled for it beforehand. But R. Oshaia taught: 'A man can go to a shepherd to whom he is accustomed to go and he gives him a sheep for his Passover sacrifice, and he sanctifies it and fulfils his obligation therewith? — There too, since he is accustomed to go to him, he [the shepherd] does indeed sanctify it beforehand.<span class="x" onmousemove="('comment',' I.e., the shepherd sanctifies it on the festival even on his behalf. ');">²⁵</span> But he states, 'he sanctifies it'?<span class="x" onmousemove="('comment',' l.e., when he receives it. ');">²⁶</span>

Orchot Tzadikim