פירוש על קידושין 69:5

The Papunians, those from a place called Papuna, have another source for the exemption of women from all positive time-bound commandments. The verse in Exodus compares the Torah to tefillin. And since we know that women are exempt from tefillin (because tefillin is compared to Torah study), women are exempt from all such mitzvoth. And if they are exempt from time-bound commandments, they must be obligated in non-time bound ones.