Reference for Makkot 34:2

אמר רבא דילידא אימיה כר"ש תיליד ואי לא לא תיליד ואע"ג דאית להו פירכא

Rava said, if a mother is giving birth, she should give birth like Rebbi Shimon, (and if not, then she should not give birth). And this is even though there is a refutation.

Jastrow