Mishkat al-Masabih #445

Abu Huraira said that a man told God’s messenger that he sailed on the sea taking a small quantity of water with him. As he would suffer from thirst if he used this for ablution, he asked whether he might use sea water for that purpose, and received the reply, “Its water is pure, and what dies a natural death in it is lawful food.” Malik, Tirmidhi, Abu Dawud, Nasa'i, Ibn Majah and Darimi transmitted it.