Sahih Bukhari
Sahih Bukhari Volume 006, Book 060, Hadith Number 015.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 60. Prophetic Commentary on the Qur'an (Tafseer of The Prophet (PBUH))
Narrated By Ibn 'Umar : While some people were offering Fajr prayer in the Quba' mosque, some-one came and said, "Allah has revealed to the Prophet Qur'anic instructions that you should face the Ka'ba (while praying) so you too, should face it." Those people then turned towards the Ka'ba.