Sayyiduna al-Mughirah bin Abi Burdah heard Sayyiduna Abu Hurayrah (may Allah be pleased with him) say that a man asked the Messenger of Allah (peace and blessings be upon him): O Messenger of Allah! We travel by sea and take a small amount of water with us; if we perform ablution with it, we will remain thirsty. May we perform ablution with sea water? The Messenger of Allah (peace and blessings be upon him) said: "Yes, its water is pure and its dead (animals) are lawful."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1