Musnad Ahmad 33:895

Abu al-Qasim ibn Abi al-Zinad narrated to us, Ishaq ibn Hazim informed me, from Abu Miqsam—meaning Ubayd Allah ibn Miqsam—from Jabir ibn Abd Allah, from the Prophet, may Allah bless him and grant him peace, who said regarding the sea: "Its water is purifying, and its dead [creatures] are lawful."