Sa'id bin Salmah bin Aby سعيد بن سلمة بن أبي · The Book on Purification

"A man asked Allah's Messenger 'O Messenger of Allah! We sail the seas, and we only carry a little water with us. If we use it for Wudu then we will go thirsty. So shall we perform Wudu from the (water of the) sea?' Allah's Messenger said: 'Its water is pure, and its dead are lawful.'"