Mishkat al-Masabih 19 Jihad كتاب الجهاد 51

وَعَن أم حرَام عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «الْمَائِدُ فِي الْبَحْرِ الَّذِي يُصِيبُهُ الْقَيْءُ لَهُ أَجْرُ شَهِيدٍ وَالْغَرِيقُ لَهُ أَجْرُ شَهِيدَيْنِ» . رَوَاهُ أَبُو دَاوُد

Umm Haram reported the Prophet as saying, “He who becomes sick on a stormy sea will have the reward of a martyr, and he who is drowned will have the reward of two martyrs.” Abu Dawud transmitted it.