Sahih Al Bukhari – Book of Shortening The Prayers (At-Taqseer)
Volumn 002, Book 020, Hadith Number 194.
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Narated By Abu Huraira RA : The Prophet (p.b.u.h) said, "It is not permissible for a woman who believes in Allah and the Last Day to travel for one day and night except with a Mahram."