Sahih Muslim Book 7, Hadith Number 3108.

Chapter : Travelling of a woman with her Mahram for Hajj, etc.

Abu Sa’id al-Khudri (Allah be pleased with him) reported Allah’s Messenger (may peace be upon him) as saying: It is not lawful for a woman believing in Allah and the Hereafter to undertake journey extending over three days or more, except when she is in the company of her father, or her son, or her husband, or her brother, or any other Mahram.