Musannaf Ibn Abi Shayba 3:3828

Yazid ibn Harun narrated to us, from Habib, from Amr ibn Haram, who said: Jabir ibn Zayd was asked about a man who prays in a *jubba* (outer garment) alone, or a thick shirt that covers his *awrah* (private parts), with nothing else on him. He said: There is no harm in it.