وَحَدَّثَنِي مَالِكٌ، عَنْ سَعِيدِ بْنِ أَبِي سَعِيدٍ الْمَقْبُرِيِّ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخَرِ تُسَافِرُ مَسِيرَةَ يَوْمٍ وَلَيْلَةٍ إِلاَّ مَعَ ذِي مَحْرَمٍ مِنْهَا ‏"‏ ‏.‏

Malik related to me from Said ibn Abi Said al-Maqburi from AbuHurayra that the Messenger of Allah, may Allah bless him and grant himpeace, said, "It is not halal for a woman who believes in Allah andthe Last Day to travel the distance of a day and night without a manwho is her mahram." Translation Not Available

Book reference: Muwatta Imam Malik Book 54 Hadith 1803
Web reference: Muwatta Imam Malik Book 54 Hadith 37