Reference for Bekhorot 64:3
אימא
But why not say: Make it bear on the subject of a firstling? - [It is reasonable to maintain that] the word ge'ulah used in connection with haramim is [to be applied to tithing since the identical word] ge'ulah [is used with reference to tithing] as with the former.<span class="x" onmousemove="('comment',' Rashi for various reasons rejects this version and gives the following version: Without the analogy between tithing and haramim one can infer that tithing must not be sold, for the text 'It shall not be sold' in connection with haramim is not necessary, for if haramim are in the possession of the owners then they are holy, and if in the possession of the priest, then they are hullin. We therefore, declares Raba, maintain that the text 'It shall not be sold' refers to tithing.');"><sup>1</sup></span>