While some people were offering Fajr prayer at Quba mosque, someone came to them and said, "Qur'anic literature" has been revealed to Allah's Messenger (ﷺ) tonight, and he has been ordered to face the Ka`ba (of Mecca) so you too, should turn your faces towards it. Their faces were then towards Sham (Jerusalem), so they turned towards the Qibla (i.e. Ka`ba of Mecca).