Sahih Bukhari Volume 003, Book 027, Hadith Number 022.
Narated By Al-Aswad : Abdullah the slave of Asma bint Abu Bakr, told me that he used to hear Asma', whenever she passed by Al-Hajun, saying, "May Allah bless His Apostle Muhammad. Once we dismounted here with him, and at that time we were traveling with light luggage; we had a few riding animals and a little food ration. I, my sister, 'Aisha, Az-Zubair and such and such persons performed 'Umra, and when we had passed our hands over the Ka'ba (i.e. performed Tawaf round the Ka'ba and between As-Safa and Al-Marwa) we finished our lhram. Later on we assumed Ihram for Hajj the same evening."