Narrated Ibn Abbas:

That he heard the Prophet saying, "It is not permissible for a man to be alone with a woman, and no lady should travel except with a Muhram (i.e. her husband or a person whom she cannot marry in any case for ever;
e.g. her father, brother, etc.)." Then a man got up and said, "O Allah's Apostle! I have enlisted in the army for such-and-such Ghazwa and my wife is proceeding for Hajj." Allah's Apostle ﷺ said, "Go, and perform the Hajj with your wife."

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، عَنْ أَبِي مَعْبَدٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ أَنَّهُ سَمِعَ النَّبِيَّ ﷺ يَقُولُ " لاَ يَخْلُوَنَّ رَجُلٌ بِامْرَأَةٍ، وَلاَ تُسَافِرَنَّ امْرَأَةٌ إِلاَّ وَمَعَهَا مَحْرَمٌ ". فَقَامَ رَجُلٌ فَقَالَ يَا رَسُولَ اللَّهِ، اكْتُتِبْتُ فِي غَزْوَةِ كَذَا وَكَذَا، وَخَرَجَتِ امْرَأَتِي حَاجَّةً. قَالَ " اذْهَبْ فَحُجَّ مَعَ امْرَأَتِكَ ".