Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that some people came to the Messenger of Allah (peace and blessings be upon him) and said: "We fish at sea and we have (a little) fresh water with us. We fear thirst. Is it proper for us to perform ablution with the salty water of the sea?" He (peace and blessings be upon him) said: "Yes! Perform ablution with it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 5