Musnad Ahmad 27:346

Waki’ narrated to us, from Sufyan, from ‘Abdullah ibn Dinar, from Ibn ‘Umar, who said: While the people were in the Mosque of Quba’ performing the morning prayer, a comer came to them and said: "Indeed, the Messenger of Allah (may Allah bless him and grant him peace) has had the Quran revealed to him, and he has been directed toward the Kaaba." He said: So they turned [toward the Kaaba].