Reference for Pesachim 52:9
אפה בו את הפת רבי אומר הפת אסורה וחכמים אומרים הפת מותרת בישלה על גבי גחלים דברי הכל מותר
This is [indeed] a refutation. AND ONE MAY NOT FIRE etc. Our Rabbis taught: If an oven was fired with the shells of 'orlah'<span class="x" onmousemove="('comment',' I.e.,the shells of nuts of 'orlah'.');"><sup>16</sup></span> or with the stubble of kil'ayim of the vineyard, if new, it must be demolished; if old, it must be allowed to cool.<span class="x" onmousemove="('comment',' 'New' means that the oven has never been used yet. Before it is fit for use it must be burnt through so as to harden it, and if this was done with the shells of 'orlah', the oven must be demolished, since it was made fit with prohibited fuel. But if it had been used before, the only benefit is that it is now hot: hence that benefit must be forfeited by allowing the oven to cool without using its heat.');"><sup>17</sup></span>