Sahih Bukhari
Prayers (Salat)
Volume: 001 / Book Number: 008 / Hadith Number: 397
Narrated 'Abdullah bin 'Umar:
While the people were offering the Fajr prayer at Quba (near Medina), someone came to them and said: "It has been revealed to Allah's Apostle tonight, and he has been ordered to pray facing the Ka'ba." So turn your faces to the Ka'ba. Those people were facing Sham (Jerusalem) so they turned their faces towards Ka'ba (at Mecca).