Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) reported on the authority of Sayyiduna Bilal (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) prayed two rak'ahs in it (the Ka'bah).
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1028