Sahih Muslim 1338
Sahih Muslim · Book 15: The Book of Pilgrimage · A woman travelling with a Mahram for Hajj and other purposes
'Abdullah b. Umar (Allah -be pleased with them) reported Allah's Apostle (ﷺ) as saying:
وَحَدَّثَنَا مُحَمَّدُ بْنُ رَافِعٍ ، حَدَّثَنَا ابْنُ أَبِي فُدَيْكٍ ، أَخْبَرَنَا الضَّحَّاكُ ، عَنْ نَافِعٍ ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ تُسَافِرُ مَسِيرَةَ ثَلاَثِ لَيَالٍ إِلاَّ وَمَعَهَا ذُو مَحْرَمٍ " .
It is not lawful for a woman who believes in Allah and the Hereafter to travel for more than three nights journey except when there is a Mahram with her.