Travel of a woman more than a barīd without a maḥram

Answer—and Allah is the Granter of success: It has come in the ḥadīth from the Prophet—May Allah bless him and his family and grant them peace—“It is not lawful for a woman who believes in Allah and the Last Day to travel a barīd except with a kinsman who is a maḥram.” This is the wording of the ḥadīth—or its meaning. In another narration: “that she travel three days …,” etc.
The apparent sense of this narration is that it is not permissible for a woman to travel a barīd without a maḥram, even with a group of women.
What appears to me, however, is permissibility—if there is safety from temptation (fitnah). The proof is what is narrated: that the Commander of the Faithful ʿAlī b. Abī Ṭālib—peace be upon him—sent ʿĀʾishah, after the Battle of the Camel, to Madinah with a caravan carrying swords and spears. When ʿĀʾishah reached Madinah with the caravan, she said to them, in substance: “Does ʿAlī b. Abī Ṭālib feel no shame—he has violated my privacy by sending me with unrelated men!” When the caravan heard her words, they removed their garments and turbans—and behold, they were women … etc. This story is well known regarding the Commander of the Faithful—peace be upon him.
Moreover, a woman’s journey of a barīd or more is not prohibited in itself, but due to another matter—namely, fear of temptation and exposure to prohibited things. If the woman is safe from that in her journey with a number of women, then there is no impediment to permitting travel beyond a barīd.
If it be said: The Wise Lawgiver tied the ruling to travel and made it contingent upon it, and did not tie it to what you have mentioned—so as to block the means to temptation and close the doors to crime; travel without a maḥram is among the likely contexts of temptation. If the matter is thus, then it is not permissible to attach the ruling to the wisdom (which the theorists call the indicator), such that the ruling is established with its presence and falls with its absence. Upon this the scholars, past and present, have proceeded: they adduce as the reason for the shortening of the four-unit prayers, or its permissibility, the very fact of travel—not hardship, whether or not hardship occurs with travel; and likewise regarding permissibility of combining prayers and of breaking the fast.
We say: The matter is as you have mentioned, were it not for the presence of what attests to what we said—namely, what was just cited from the Commander of the Faithful, for it indicates the permissibility of a woman’s traveling with trustworthy, reliable women.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1