Sahih Muslim Book 7, Hadith Number 2859.

Chapter : Permissibility of Umra during the mouth of Hajj.

Ibn ‘Abbas (Allah be pleased with them)’is reported to have said: The Messenger of Allah (may peace be upon him) put on Ihram for Hajj. When four days of Dhu’l-Hijja were over, he led the dawn prayer, and when the prayer was complete, he said: He who wants to change it to Umra may do so.