Sahih Muslim Book 7, Hadith Number 2864.

Chapter : Permissibility of Umra during the mouth of Hajj.

Abu Jam at al-Dubu’i reported: I performed Tamattu’ but the people discouraged me to do so. I came to Ibn ‘Abbas and asked him about it. He ordered me to do so. I came to the House (Ka’ba) and slept. I saw a visitant in the dream who said: ‘Umra is acceptable and so is the Hajj performed for God’s sake. I came to Ibn Abbas and informed him about that Which I saw in the dream whereupon he said: Allah is the Greatest, Allah is the Greatest This is the Sunnah of Abu’l-Qasim (the Holy Prophet) (may peace be upon him).