Musannaf Ibn Abi Shayba 3:4205

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Hawshab ibn ‘Aqil al-‘Abdi, he said: Al-Hasan was asked about the Magian sailor who is in front of the people on the ship while they are praying. He said: There is no harm in it. And he is standing (sleeping). He said: He prays behind him, even if he is standing.