Sahih Bukhari Volume 3, Book 51, Hadith 2594

حَدَّثَنَا حِبَّانُ بْنُ مُوسَى، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا أَرَادَ سَفَرًا أَقْرَعَ بَيْنَ نِسَائِهِ، فَأَيَّتُهُنَّ خَرَجَ سَهْمُهَا خَرَجَ بِهَا مَعَهُ، وَكَانَ يَقْسِمُ لِكُلِّ امْرَأَةٍ مِنْهُنَّ يَوْمَهَا وَلَيْلَتَهَا، غَيْرَ أَنَّ سَوْدَةَ بِنْتَ زَمْعَةَ وَهَبَتْ يَوْمَهَا وَلَيْلَتَهَا، لِعَائِشَةَ زَوْجِ النَّبِيِّ صلى الله عليه وسلم تَبْتَغِي بِذَلِكَ رِضَا رَسُولِ اللَّهِ صلى الله عليه وسلم‏.‏

Narrated By 'Aisha : Whenever Allah's Apostle 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 Zam'a gave up her (turn) day and night to 'Aisha, the wife of the Prophet in order to seek the pleasure of Allah's Apostle (by that action).