Sunan Ibn Majah Book 1, Hadith 386

حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا مَالِكُ بْنُ أَنَسٍ، حَدَّثَنِي صَفْوَانُ بْنُ سُلَيْمٍ، عَنْ سَعِيدِ بْنِ سَلَمَةَ، - هُوَ مِنْ آلِ ابْنِ الأَزْرَقِ - أَنَّ الْمُغِيرَةَ بْنَ أَبِي بُرْدَةَ، - وَهُوَ مِنْ بَنِي عَبْدِ الدَّارِ - حَدَّثَهُ أَنَّهُ، سَمِعَ أَبَا هُرَيْرَةَ، يَقُولُ جَاءَ رَجُلٌ إِلَى رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّا نَرْكَبُ الْبَحْرَ وَنَحْمِلُ مَعَنَا الْقَلِيلَ مِنَ الْمَاءِ فَإِنْ تَوَضَّأْنَا بِهِ عَطِشْنَا أَفَنَتَوَضَّأُ مِنْ مَاءِ الْبَحْرِ فَقَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ هُوَ الطَّهُورُ مَاؤُهُ الْحِلُّ مَيْتَتُهُ ‏"‏ ‏.‏

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)