Midrasch zu Tehillim 79:11
תָּ֤ב֣וֹא לְפָנֶיךָ֮ אֶנְקַ֪ת אָ֫סִ֥יר כְּגֹ֥דֶל זְרוֹעֲךָ֑ ה֝וֹתֵ֗ר בְּנֵ֣י תְמוּתָֽה׃
Möge vor dich kommen das Stöhnen der Gefesselten: mit deiner großen Macht erhalte die dem Tode Geweihten.
Mekhilta DeRabbi Shimon Ben Yochai
"That the Torah of the Lord be in thy mouth" -- to exclude women [from tefillin]. What is exemplary about tefillin? They are a positive time-triggered commandment from which women are exempt. So too, are women exempt from all positive time-triggered commandments.
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