Ubaydullah bin Abdullah bin Utbah narrates from Sayyidah Aishah (may Allah be pleased with her), (concerning the time) when the slanderers said what they said, and then Allah, the Lord of Might, declared her innocent. Imam al-Zuhri (may Allah have mercy on him) said: A group narrated (this) to me from Sayyidah Aishah (may Allah be pleased with her), some of whom retained it better than others, and I retained the hadith of each one of them who narrated to me from Sayyidah Aishah (may Allah be pleased with her), for their accounts confirm one another. They stated that Sayyidah Aishah (may Allah be pleased with her) said: "When the Messenger of Allah (peace and blessings be upon him) intended to travel, he would cast lots among his wives, and whoever's lot came out would go with him (peace and blessings be upon him)." She said: "He (peace and blessings be upon him) cast lots during a military expedition, and my lot came out, so I set out with him (peace and blessings be upon him), and (by that time) the verses of hijab had been revealed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14768