Sahih Bukhari Volume 003, Book 044, Hadith Number 683.
Narated By Ibn 'Abbas : The Prophet (along with his companions) reached Mecca in the morning of the fourth of Dhul-Hijja assuming Ihram for Hajj only. So when we arrived at Mecca, the Prophet ordered us to change our intentions of the Ihram for'Umra and that we could finish our Ihram after performing the 'Umra and could go to our wives (for sexual intercourse). The people began talking about that. Jabir said surprisingly, "Shall we go to Mina while semen is dribbling from our male organs?" Jabir moved his hand while saying so. When this news reached the Prophet he delivered a sermon and said, "I have been informed that some peoples were saying so and so; By Allah I fear Allah more than you do, and am more obedient to Him than you. If I had known what I know now, I would not have brought the Hadi (sacrifice) with me and had the Hadi not been with me, I would have finished the Ihram." At that Suraqa bin Malik stood up and asked "O Allah's Apostle! Is this permission for us only or is it forever?" The Prophet replied, "It is forever." In the meantime 'Ali bin Abu Talib came from Yemen and was saying Labbaik for what the Prophet has intended. (According to another man, 'Ali was saying Labbaik for Hajj similar to Allah's Apostle's). The Prophet told him to keep on the Ihram and let him share the Hadi with him.