Midrash for Chullin 268:2

כי אתא רבין אמר

he is exempt.<span class="x" onmousemove="('comment',' In all these cases the doubt was whether at the material time, i.e., when the obligation to make these presents to the priest fell due, this man was already a proselyte or not. Since, however, these are all monetary considerations we adopt the lenient view and leave it to the priest who is the claimant to establish his claim.');">²</span>

Sifrei Devarim