Sahih Muslim Book 7, Hadith Number 2777.

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) said: Some among us put on Ihram for Hajj alone (Hajj Mufrad); some of us for Hajj and Umra together (Qiran), and some of us for Tamattal (first for Umra and after completing it for Haii).