Reference for Pesachim 65:9

מנא הני מילי אמר רב נחמן בר יצחק אמר קרא (דברים יח, ד) תתן לו ולא לאורו

R'Huna son of R'Joshua objected: One must not separate terumah from unclean [produce] for clean; yet if he separates [thus] unwittingly, his terumah is valid. Yet why? Let us say, 'for him but not for his light'? - There is no difficulty: There it enjoyed a time of fitness,<span class="x" onmousemove="('comment',' Before it became unclean it was fit to be separated as terumah.');">¹⁵</span>

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