Abdullah bin Amr (may Allah be pleased with them both) says: The Messenger of Allah (peace and blessings be upon him) said: "No one should travel by sea except one going on a military expedition, a pilgrim performing Hajj or one performing Umrah. Indeed, beneath the sea is fire, and beneath the fire is sea."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8662