Sahih Muslim Book 007, Hadith Number 3070.
Chapter : The merit of entering the ka'ba for a pilgrim and observing of prayer in it.
Ibn Umar (Allah be pleased with them) reported: Allah's Messenger (may peace be upon him) came during the year of Victory on the she-camel of Usama b. Zaid until he made her kneel down in the courtyard of the Ka'ba (and got down). He then sent for 'Uthman b. Talha and said: Bring me the key. He went to his mother and she refused to give that to him. He said: By Allah, give that to him or this sword would be thrust into my side. So she gave that to him, and he came with that to Allah's Apostle (may peace be upon him) and gave that to him, and he opened the door. The rest of the Hadith is the same as the above one.