Reference for Bekhorot 63:46

(ויקרא יד, לט) ושב הכהן ובא הכהן זו היא שיבה זו היא ביאה

Why not say that the text 'It shall not be redeemed' in connection with tithing is required for its own sake, while the text 'Thou shalt not redeem' referring to a firstling is free for interpretation?<span class="x" onmousemove="('comment',' That just as in the case of haramim selling is forbidden, so a firstling must not be sold.');">²⁷</span>

Jastrow