Sahih Bukhari Volume 7, Book 62, Hadith Number 138.

Narrated By al-Qasim : ‘Aisha said that whenever the Prophet intended to go on a journey, he drew lots among his wives (so as to take one of them along with him). During one of his journeys the lot fell on ‘Aisha and Hafsa. When night fell the Prophet would ride beside ‘Aisha and talk with her. One night Hafsa said to ‘Aisha, “Won’t you ride my camel tonight and I ride yours, so that you may see (me) and I see (you) (in new situation)?” ‘Aisha said, “Yes, (I agree.)” So ‘Aisha rode, and then the Prophet came towards ‘Aisha’s camel on which Hafsa was riding. He greeted Hafsa and then proceeded (beside her) till they dismounted (on the way). ‘Aisha missed him, and so, when they dismounted, she put her legs in the Idhkhir and said, “O Lord (Allah)! Send a scorpion or a snake to bite me for I am not to blame him (the Prophet).