Reference for Arakhin 10:3

טעמא דרבי מאיר התם דגזר פחות מבן חודש אטו בן חודש אבל הכא דליכא למיגזר אימא לא קמ"ל

where no such decree is warranted, one might [assume that R'Meir would] not [rule thus], therefore we are informed that R'Meir's reason is that no man utters his words at random, so that the same rule applies in both cases.

Jastrow