Sahih Bukhari
Accepting Information Given by a Truthful Person
Volume: 009 / Book Number: 091 / Hadith Number: 357
Narrated 'Abdullah bin 'Umar:
While the people were at Quba offering the morning prayer, suddenly a person came to them saying, "Tonight Divine Inspiration has been revealed to Allah's Apostle and he has been ordered to face the Ka'ba (in prayers): therefore you people should face it." There faces were towards Sham, so they turned their faces towards the Ka'ba (at Mecca).