Reference for Pesachim 118:7

הוא מותיב לה והוא מפרק לה כשנתותרו

as though they were defiled or lost. For it was taught: You might think that if the emurim were defiled or lost, the priests have no right to the breast or the thigh, therefore it is stated, 'But the breast s be Aaron's and his sons', in all cases.

Jastrow