Musannaf Ibn Abi Shayba 11:175

Waki’ narrated to us, from Sufyan, from Ibrahim ibn Muhajir, from Tariq ibn Shihab, who said: ‘Abdullah said: “Indeed, among those who drown in the seas, and those who fall from the mountains, and those whom the beasts of prey eat, are martyrs before Allah on the Day of Resurrection.”