Mishkat al-Masabih 19 Jihad كتاب الجهاد 50

وَعَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَا تَرْكَبِ الْبَحْرَ إِلَّا حَاجًّا أَوْ مُعْتَمِرًا أَوْ غَازِيًا فِي سَبِيلِ اللَّهِ فَإِنَّ تَحْتَ الْبَحْرِ نَارًا وَتَحْتَ النَّارِ بَحْرًا» . رَوَاهُ أَبُو دَاوُدَ

‘Abdallah b. ‘Amr reported God’s Messenger as saying, “Do not sail on the sea except when going to perform the hajj , or the ‘umra , or when fighting in God’s path, for under the sea there is a fire and under the fire there is a sea.” Abu Dawud transmitted it.