Musannaf Ibn Abi Shayba 3:2606

Abu Bakr narrated to us, he said: Hafs bin Ghiyath narrated to us, from Ibn Jurayj, from ‘Ata’, who was asked about a people whose ship broke while they were in the water and the prayer overtook them. He said: "They should gesture [for the prayer] with a gesture." He was asked: "If they emerge naked?" He said: "They should pray sitting."