Narrated Ibn `Umar:
While some people were offering Fajr prayer in the Quba' mosque, some-one came and said, "Allah has revealed to the Prophet (ﷺ) 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.
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 15
Arabic reference: Book 65, Hadith 4488