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.
Sahih Muslim Book 15, Hadith 464
← Previous Hadith " More than three (days)." Ibn Numair narrated on the authority of his father, (and the words are):" Three (days) except (when) she has a Mahram with her."

Sahih Muslim Book 15, Hadith 463 Next Hadith → I heard a hadith from Abu Sa'id (Allah be pleased with him) and it impressed me (very much), so I said to him: Did you hear it (yourself) from Allah's Messenger (ﷺ)? Thereupon he said: (Can) I speak of anything about Allah's Messenger (ﷺ) which I did not bear? He said: I heard Allah's Messenger (ﷺ) saying: Do not set out on a journey (for religious devotion) but for the three mosques-for this mosque of mine (at Medina) the Sacred Mosque (at Mecca), and the Mosque al-Aqsa (Bait al-Maqdis), and I heard him saying also: A woman should not travel for two days duration, but only when there is a Mahram with her or her husband.

Sahih Muslim Book 15, Hadith 465