Abu Hurairah said: “A man asked the prophet (peace be upon him): ‘O Messenger of Allah, we travel by sea and we take a little water with us, but if we use it for Wudu’, we will go thirsty. Can we perform Wudu’ with seawater?’ The Messenger of Allah (peace be upon him) said: ‘Its water is a means of purification and its dead meat is permissible.'”
Sunan an-Nasa’I, Vol. 1, Book 2, Hadith 8