Whenever the Prophet (may Allah's peace and blessings be upon him) intended to go on a journey, he would cast lots among his wives and would take the one on whom the lot fell
Authentic hadithعن عائشة رضي الله عنها قالت: «كان النبي صلى الله عليه وسلم إذا أراد أَنْ يَخْرُج أَقْرَعَ بَيْن نِسائه، فأيَّتُهُنَّ يَخْرُج سَهْمُها خَرَج بها النبي صلى الله عليه وسلم ، فَأَقْرَعَ بَيْنَنَا في غَزْوَةٍ غَزَاها، فَخَرج فيها سَهْمِي، فخَرَجْتُ مع النبي صلى الله عليه وسلم بَعْد ما أُنْزِلَ الحِجابُ».
‘Ā'ishah (may Allah be pleased with her) reported: Whenever the Prophet (may Allah's peace and blessings be upon him) intended to go on a journey, he would cast lots among his wives and would take the one on whom the lot fell. Once, before setting out for a battle, he drew lots among us and the lot fell to me; so I went with the Prophet, may Allah's peace and blessings be upon him; and that happened after the revelation of (the verse on) Hijāb.
Explanation
‘Ā'ishah (may Allah be pleased with her) reported in this Hadīth that the Prophet (may Allah's peace and blessings be upon him) would cast lots to pick one of his wives to accompany him whenever he wanted to go on a journey. This was to ensure perfect justice and grant assurance and comfort to his wives' hearts. In one of his battles, the Banu al-Mustaliq Battle, the Prophet drew lots and ‘Ā'ishah's name came out so she traveled with him. She mentioned that this took place after Allah, the Almighty, had prescribed Hijāb. It is obvious that the Prophet (may Allah's peace and blessings be upon him) would cast lots the next time he would go on a journey among the remaining wives, as the one who accompanied him in the previous journey had already taken her share. When only one remained, he would take her without casting lots.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).