Sahih Bukhari Volume 3, Book 48, Hadith Number 853.

Narated 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.