Sahih Bukhari | Volume 3 | Hadith Number 853

Narrated by 'Aisha
Whenever Allah's Apostle intended to go on a journey, he used to draw lots among his wives and would take with him the one on whom the lot fell. He also used to fix for everyone of his wives a day and a night, but Sauda bint Zam'a gave her day and night to 'Aisha, the wife of the Prophet intending thereby to please Allah's Apostle.