It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) used to say: O women of Islam! Let not any neighbor consider insignificant the thing sent by her neighbor, even if it is only a hoof of a goat. And it is not lawful for any woman "who believes in Allah and the Last Day" to travel for even one day without a mahram from her family.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10575