Reference for Bekhorot 64:19

לאחר שחיטה דאקיל ליה קדושתיה מיפריק

I migh have thought that it cannot indeed be sold, since he performed a secular action [in exchanging], but it can be redeemed, because its money enters [the coffers of] the Sanctuary, the Divine Law therefore writes 'It shall not be redeemed' teaching that it can neither be sold nor redeemed.

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