Musannaf Ibn Abi Shayba 3:4202

Hushaym narrated to us, from Ayyub Abu al-Ala, who said: I heard Ata, and he was asked about a sailor who is in a ship, and his family is with him in it, and it is his home, and he travels in it. He said: He prays four [rak'ahs] in it.