Reference for Chullin 149:48

א"ל

Raba said: Even according to him who permits [the other without slaughtering] it is permitted, for the Divine Law permits [the foetus] by [the slaughtering of any two out of] four organs.<span class="x" onmousemove="('comment',' I.e., either the two organs of its dam or its own two organs, for the foetus is rendered permitted either by its own slaughtering or by the slaughtering of its dam.');">³⁰</span>

Jastrow