Sahih Bukhari Volume 003, Book 027, Hadith Number 011.
Narated By 'Aisha : We set out along with Allah's Apostle shortly before the appearance of the new moon (crescent) of the month of Dhi-l-Hijja and he said to us, "Whoever wants to assume Ihram for Hajj may do so; and whoever wants to assume Ihram for 'Umra may do so. Hadn't I brought the Hadi (animal for sacrificing) (with me), I would have assumed Ihram for 'Umra." ('Aisha added,): So some of us assumed Ihram for 'Umra while the others for Hajj. I was amongst those who assumed Ihram for 'Umra. The day of 'Arafat approached and I was still menstruating. I complained to the Prophet (about that) and he said, "Abandon your 'Umra, undo and comb your hair, and assume Ihram for Hajj;." When it was the night of Hasba, he sent 'Abdur Rahman with me to At-Tan'im and I assumed Ihram for 'Umra (and performed it) in lieu of my missed 'Umra.