Musnad Ahmad 32:357

Abu Amir narrated to us, Abd al-Rahman—meaning Ibn Abi al-Mawal—narrated to us, from Musa ibn Ibrahim ibn Abi Rabi'ah, from his father, who said: We entered upon Anas ibn Malik while he was praying in a single garment, wrapping himself in it, while his rida' (outer garment/shawl) was placed aside. When he finished, we said to him: "Do you pray while your rida' is placed aside?" He said: "Thus I saw the Prophet, may Allah bless him and grant him peace, praying."