Sahih Bukhari
Prayers (Salat)
Volume: 001 / Book Number: 008 / Hadith Number: 391
Narrated Ibn Abbas:
When the Prophet entered the Ka'ba, he invoked Allah in each and every side of it and did not pray till he came out of it, and offered a two-Rak'at prayer facing the Ka'ba and said, "This is the Qibla."