Musnad Ahmad 26:54

Abu Bakr narrated to us, 'Asim narrated to us, from Zirr, from 'Abdullah, who said: The Messenger of Allah (ﷺ) said: "Perhaps you will encounter people who pray the prayer outside of its time. So if you encounter them, pray in your houses at the time that you know, then pray with them, and make it a voluntary prayer (nafilah)."