It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: If people knew the harm of traveling alone, then no one would travel alone at night.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6014
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ: 2998.