Whenever Messenger of Allah ﷺ wanted to go on a journey, he would draw lots as to which of his wives would accompany him. He would take her whose name came out. He used to fix for each of them a day and a night. But Sauda bint Zamʿa gave up her (turn) day and night to ʿAisha, the wife of the Prophet in order to seek the pleasure of Messenger of Allah ﷺ (by that action). (Using translation from Bukhārī 2593)
كَانَ رَسُولُ اللهِ ﷺ إِذَا أَرَادَ سَفَرًا أَقْرَعَ بَيْنَ نِسَائِهِ فَأَيَّتُهُنَّ خَرَجَ سَهْمُهَا خَرَجَ بِهَا مَعَهُ وَكَانَ يَقْسِمُ لِكُلِّ امْرَأَةٍ مِنْهُنَّ يَوْمَهَا وَلَيْلَتَهَا غَيْرَ أَنَّ سَوْدَةَ بِنْتَ زَمْعَةَ كَانَتْ وَهَبَتْ يَوْمَهَا وَلَيْلَتَهَا لِعَائِشَةَ زَوْجِ النَّبِيِّ ﷺ تَبْتَغِي بِذَلِكَ رِضَا النَّبِيِّ ﷺ