Sahih Muslim
The Book of Pilgrimage (Kitab Al-Hajj)
Book Number: 007 / Hadith Number: 2843
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."