Reference for Sotah 59:1

שלישי הבא מחמת שני דשני גופיה אסור בחולין אינו דין שעושה רביעי בקודש

then that which is unclean in the third degree through contact with what is unclean in the second degree — the second degree which is itself forbidden in the case of non-holy food<span class="x" onmousemove="('comment',' Non-holy food can become unclean in the second degree. ');">¹</span>

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