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).'"  

أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ يَقُولُ جَاءَ رَجُلٌ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّا نَرْكَبُ الْبَحْرَ وَنَحْمِلُ مَعَنَا الْقَلِيلَ مِنَ الْمَاءِ فَإِنْ تَوَضَّأْنَا بِهِ عَطِشْنَا أَفَنَتَوَضَّأُ مِنْ مَاءِ الْبَحْرِ فَقَالَ رَسُولُ اللَّهِ ﷺ هُوَ الطَّهُورُ مَاؤُهُ الْحِلُّ مَيْتَتُهُ  

"I was fishing and I had a vessel with me in which I kept water, and I used seawater for ablution. I mentioned that to the Messenger of Allah and he said: 'Its water is a means of purification, and its dead meat is permissible.'"  

كُنْتُ أَصِيدُ وَكَانَتْ لِي قِرْبَةٌ أَجْعَلُ فِيهَا مَاءً وَإِنِّي تَوَضَّأْتُ بِمَاءِ الْبَحْرِ فَذَكَرْتُ ذَلِكَ لِرَسُولِ اللَّهِ ﷺ فَقَالَ هُوَ الطَّهُورُ مَاؤُهُ الْحِلُّ مَيْتَتُهُ  

The Prophet was asked about seawater, and he said: "Its water is a means of purification, and its dead meat is permissible." (Hasan) Another chain with similar wording.  

أَنَّ النَّبِيَّ ﷺ سُئِلَ عَنْ مَاءِ الْبَحْرِ فَقَالَ هُوَ الطَّهُورُ مَاؤُهُ الْحِلُّ مَيْتَتُهُ قَالَ أَبُو الْحَسَنِ بْنُ سَلَمَةَ حَدَّثَنَا عَلِيُّ بْنُ الْحَسَنِ الْهِسِنْجَانِيُّ حَدَّثَنَا أَحْمَدُ بْنُ حَنْبَلٍ حَدَّثَنَا أَبُو الْقَاسِمِ بْنُ أَبِي الزِّنَادِ حَدَّثَنِي إِسْحَاقُ بْنُ حَازِمٍ عَنْ عُبَيْدِ اللَّهِ هُوَ ابْنُ مِقْسَمٍ عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ أَنَّ النَّبِيَّ ﷺ فَذَكَرَ نَحْوَهُ