Sahih Muslim Book 7, Hadith Number 2843.

Chapter : Ifrad and Qiran (combining Hajj and Umra in one Ihram) in the performance of pilgrimage.

Nafi’ thus reported on the authority of Ibn Umar: We entered into the state of Ihram with Allah’s Messenger (may peace be upon him) for Hajj Mufrad and in the narration of Ibn ‘Aun (the words are): “Allah’s Messenger (may peace be upon him) entered into the state of Ihram (with the intention) of Hajj Mufrad.”