Sahih Muslim Book 7, Hadith Number 2800.
Chapter : Types of Ihram- It is permissible to enter into the state of Ihram singularly for the sake of Hajj or for tamattu’ bi’l-‘umra ila’l-Hajj or for both hajj and ‘umra together.
Jabir b. ‘Abdullah (Allah be pleased with them) reported: We set out with Allah’s Messenger (may peace be upon him) as Muhrim for Hajj. The Messenger of Allah (may peace be upon him) commanded us to make this Ihram for Umra, and some put it off (after performing ‘Umra), but the Prophet (may peace be upon him) had sacrificial animals with him, so he could not make it (this Ihram) as that of Umra.