Whenever the Prophet ﷺ intended to set out on a journey, he would draw lots among his wives, and whichever one's lot came out, he would take her with him. On one expedition he drew lots among us, and my lot came out, so I traveled with the Prophet ﷺ. This was after the verse of the veil had been revealed.
كان النبي ﷺ إذا أراد أن يخرج أقرع بين نسائه فأيتهن يخرج سهمها خرج بها النبي ﷺ، فأقرع بيننا في غزوة غزاها فخرج فيها سهمي، فخرجت مع النبي ﷺ بعد ما أنزل الحجاب.
Bukhari narrated it in the book of jihad and expeditions (2879), and Muslim narrated it in the book of repentance (2770:56), both by way of Yunus bin Yazid Ayli - and Muslim added Maamar - from Zuhri, who said, I heard Urwa bin Zubayr, Saeed bin Musayab, Alqama bin Waqqas, and Ubaydullah bin Abdullah, regarding the hadith of Ayesha, each of them narrating a portion of the account to me. She said, and then she related it. The wording given here is Bukhari's, while Muslim gave it in full, and it occurs within the story of the slander.