Reference for Chullin 262:21

ר' אלעזר בן עזריה אומר

and whatsoever is not sacred, as the shoulder, the two cheeks and the maw, is not exacted from them!<span class="x" onmousemove="('comment',' This clearly shows that the Levites are not under any obligation to give the shoulder etc. to the priests, obviously because they are not included under the term 'the people'. Why then was Rab in doubt about it?');">¹⁷</span>

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