Reference for Bekhorot 53:3

ישראל שהפריש תרומה מכריו ומצאו ישראל אחר ואמר לו

If, however, a priest [approached him] on behalf of another priest, it is forbidden.<span class="x" onmousemove="('comment',' For it looks as if the priest buys the right of the terumah on behalf of another priest, although he can claim it himself. It, therefore, comes under the category of the action of a priest who helped in the threshing floor.');">²</span>

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