From Sahih Muslim (Hadith 1180):
Anas reported:The Messenger of Allah (ﷺ) used to pray towards Bait-ul-Maqdis, that it was revealed (to him):" Indeed We see the turning of the face to heaven, wherefore We shall assuredly cause thee to turn towards Qibla which shall please thee. So turn thy face towards the sacred Mosque (Ka'ba)" (ii. 144). A person from Banu Salama was going; (he found the people) in ruk'u (while) praying the dawn prayer and they had said one rak'ah. He said in a loud voice: Listen! the Qibla has been changed and they turned towards (the new) Qibla (Ka'ba) in that very state
Reference: Muslim 1180