Reference for Yoma 68:3
ורבנן מאי אחד מיוחד שבעדרו ורבי (דברים יב, יא) מומבחר נדריך נפקא ורבנן חד בחובה וחד בנדבה וצריכי
And the Rabbis? - One speaks of freewill-[offerings], the other of obligatory [offerings] and both need special mention.<span class="x" onmousemove="('comment',' As arguments may be advanced in favour of each requiring to be of the best, to the exclusion of the other.');"><sup>7</sup></span> IF THE HIGH PRIEST WAS OLD OR OF DELICATE HEALTH etc. It was taught: R'Judah said: Lumps of wrought iron were heated on the eve of the Day of Atonement and were cast into the cold water to mitigate the coldness. But was [one] not thereby hardening them?<span class="x" onmousemove="('comment',' Which is forbidden on any holy day, how much more on the solemn Day of Atonement.');"><sup>8</sup></span> - R'Bibi said: [The heat] did not reach the hardening point.