Musannaf Ibn Abi Shayba 3:3786

Muhammad ibn Abi ‘Adi narrated to us, from Ibn ‘Awn, who said: Muhammad [ibn Sirin] was asked about a man who is on the roof of a house, praying by the prayer of the Imam during Ramadan. He said: "I do not see any harm in it, unless he is in front of the Imam."