Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.149.

Section : Sailing in Rough Weather.

It is not permissible to embark on a voyage when the sea is stormy and agitated. According to a hadith reported by Abu ‘Umran al-Jawni some of the Companions told him that the Prophet, peace be upon him, said, “Anyone who sleeps on a house-top that has no fence, and then falls and dies, he forfeits the protection of Allah, and anyone who sails while the sea is rough, and then perishes, he forfeits the protection of Allah.” (Reported by Ahmad with a sound chain of authorities).