Reference for Chullin 231:29

חיה ועוף אינן מן התורה הא מדרבנן אסירי

There is also [a Baraitha] taught to the same effect: In the place of R'Eliezer they used to cut wood [on the Sabbath] to make charcoal in order to forge an iron instrument.<span class="x" onmousemove="('comment',' Sc. the circumcision knife. R. Eliezer is of the opinion that, since the performance of the precept of circumcision supersedes the Sabbath, all the necessary requisites such as the making or preparation of the knife, or the kindling of fire to obtain warm water etc. may also be performed on the Sabbath. V. Shab. 130a.');">¹⁴</span>

Jastrow

Jastrow