Musannaf Ibn Abi Shayba 1:2041

Abu Dawud narrated to us, from Shu'bah, who said: "I used to wade through the rain, so I asked al-Hakam, and he said: 'Perform the prayer.'" He said: "And I heard Abu Ishaq saying: 'They used to wade [through the rain] and then perform the prayer, and they would not carry water jugs with them.'"