Reference for Bekhorot 36:14

טעמא דר' מאיר דלא תשתכח תורת מתנות אפילו ספק מעשר נמי קא משמע לן

but in the case of a doubtfully tithed animal, it is not so!<span class="x" onmousemove="('comment',' For the priest can only claim on the ground that it is hullin, an unconsecrated animal, since a tithed animal belongs to the owner.');">⁴</span>

Jastrow