Sahih Muslim Book 7, Hadith Number 2771.

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: We proceeded with the Messenger of Allah (may peace be upon him) during the year of the Farewell Pilgrimage. There were those amongst us who had put on Ihram for Umra, and those who had put on Ihram both for Hajj and “Umra, and those amongst us who had put on Ihram for Hajj (only), while the Messenger of Allah (may peace be upon him) had put on Ihram for Hajj (only). He who put on Ihram for Umra put it off (after performing ‘Umra), and he who had put on Ihram for Hajj or for both Hajj and ‘Umra did not put it off before the day of sacrifice (10th of Dhu’I-Hijja).