Musannaf Ibn Abi Shayba 3:3816

Zayd ibn al-Hubab narrated to us, from Mu'awiyah ibn Salih, from Musa ibn Yazid, who said: I heard Abu Umamah—and he was asked about praying in a single qamis (shirt)—and he said: "There is no harm in it." And regarding the rita (a single-piece garment/sheet), if you wrap yourself in it, there is no harm in it.