I asked ‘A’isha (ra): What is the reason that a menstruating woman completes the (obligatory) fasts (that she abandons during her monthly course). but she does not complete the prayers?
She (Hadrat ‘A’isha) answered: Are you a Haruriya?
I said: I am not a Haruriya, but I simply want to inquire.
She (Hadrat ‘A’isha) said: We passed through this (period of menstruation), and we were ordered to complete the fasts, but were not ordered to complete the prayers (during the time of Prophet Muhammad pbuh) .
Sahih Muslim 335 c
In-book : Book 3, Hadith 85