Reference for Shevuot 23:2
אלא רבנן דפרה דלמא שאני פרה דדמיה יקרין
[But again it may be urged:] Perhaps the red heifer is different, because it i expensive!<span class="x" onmousemove="('comment',' Therefore the Beth din deem it worth while to make a mental stipulation, but in the case of the daily offerings which are not expensive, the Beth din possibly do not make a mental stipulation.');"><sup>3</sup></span> - Well, then, the Rabbis [of our Mishnah] who argued with him.<span class="x" onmousemove="('comment',' Thus: Since the goats are not equal in the atonement they bring, and since you do not hold that the Beth din can make a mental stipulation that if the goat of the Day of Atonement, for example, was lost and found later, it may be offered on a subsequent festival, how according to you, can the goat set apart on one day be offered on another? These Rabbis, then, themselves hold that the Beth din can make a mental stipulation.');"><sup>4</sup></span>