Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "It is not lawful for a Muslim woman to travel a journey of one night without a mahram."
In the narrations of Sayyiduna Abu Hurayrah (may Allah be pleased with him), wherever the word 'a day' (yawman) occurs, its night is also meant, and wherever the word 'a night' (laylatan) occurs, its day is also meant.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5411