Sahih Muslim Book 7, Hadith Number 2785.

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.

‘Aisha (Allah be pleased with her) reported that the Messenger of Allah (may peace be upon him) came out on the 4th or 5th of Dhul’I-Hijja (for Pilgrimage to Mecca) and came to me, and he was very angry. I said: Messenger of Allah, who has annoyed you? May Allah cast him in fire I He said: Don’t you know that I commanded the people to do an act, but they are hesitant. (Hakam said: I think that he said: They seem to be hesitant.) And if I were to know my affair before what I had to do subsequently, I would not have brought with me the sacrificial animals, and would have bought them (at Mecca) and would have put off ihram as others have done.