Musnad Ahmad 30:1978

Husayn narrated to us, he said: Abu Uways narrated to us, Safwan ibn Sulaym, the freed slave of Humayd ibn Abd al-Rahman ibn Awf, narrated to us, from Sa'id ibn Salamah ibn al-Azraq al-Makhzumi, from al-Mughirah ibn Abi Burdah, one of the sons of Abd al-Dar ibn Qusay, from Abu Hurayrah, from the Prophet, may God bless him and grant him peace, that some people who were fishermen at sea came to him and said: "O Messenger of God, we are people of rafts, and we carry little water. If we drink from it, there is not enough left to perform ablution with, and if we perform ablution with it, there is not enough left to drink. Shall we perform ablution with sea water?" The Prophet, may God bless him and grant him peace, said: "Yes, its water is purifying, and its dead [creatures] are lawful."