It was narrated that Mughirah bin Abu Burdah, who was from the tribe of Banu 'Abdud-Dar, said that: He heard Abu Hurairah say: A man came to the Messenger of Allah and said: O Messenger of Allah, we travel by sea and carry a small amount of water with us. If we use it for ablution, we will become thirsty. Can we perform ablution with seawater?' The Messenger of Allah said: 'Its water is a means of purification, ad its dead meat is permissible. (i.e. the fish found dead in the sea).'
It was narrated that Ibn Firasi said: I was fishing and I had a vessel with me in which I kept water, and I used seawater for ablution. I mentioned that to the Messenger of Allah and he said: 'Its water is a means of purification, and its dead meat is permissible.'
It was narrated from Jabir that: The Prophet was asked about seawater, and he said: Its water is a means of purification, and its dead meat is permissible. (Hasan) Another chain with similar wording