Abu Huraira said that a man told God’s messenger that he sailed on the sea taking a small quantity of water with him. As he would suffer from thirst if he used this for ablution, he asked whether he might use sea water for that purpose, and received the reply, “Its water is pure, and what dies a natural death in it is lawful food.” Malik, Tirmidhi, Abu Dawud, Nasa'i, Ibn Majah and Darimi transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَبِي هُرَيْرَةَ قَالَ: سَأَلَ رَجُلٌ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّا نَرْكَبُ الْبَحْرَ وَنَحْمِلُ مَعَنَا الْقَلِيلَ مِنَ الْمَاءِ فَإِنْ تَوَضَّأْنَا بِهِ عَطِشْنَا أفنتوضأ من مَاء الْبَحْرِ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «هُوَ الطَّهُورُ مَاؤُهُ الْحِلُّ مَيْتَتُهُ» . رَوَاهُ مَالك وَالتِّرْمِذِيّ وَالنَّسَائِيّ وَابْن مَاجَه والدارمي
sunnah.com