Musannaf Ibn Abi Shayba 3:4206

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sharik narrated to us, from Matar, from ‘Ata’ ibn Abi Rabah, regarding the Magian (Zoroastrian) sailors who are in front of the people on the ship while they (the people) are praying. He said: There is no harm in it.