The Messenger of Allah ﷺ said, "A woman must not travel a full day's journey except in the company of a male relative she cannot marry."
حدثنا وكيع قال حدثنا ابن أبي ذئب عن سعيد بن أبي سعيد عن أبيه
قال رسول الله ﷺ لا تسافر امرأة مسيرة يوم تام إلا مع ذي محرم
Its chain of transmission is sahih. Bukhari related it in 2/54, in the chapter on shortening the prayer, on how much distance allows shortening it, as did Muslim in 2/976, no. 827, and Abu Dawud in 2/140, no. 1727.