Musnad Abu Ya'la al-Mawsili 42:224

Narrated to us Zuhayr, narrated to us Abu Mu'awiyah, from al-A'mash, from Abu Salih, from Abu Sa'id, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "It is not lawful for a woman who believes in Allah and the Last Day to travel a journey that is three days or more, unless her father, or her son, or her husband, or a mahram of hers is with her."