Musnad Ahmad 89:0

Narrated to us by Muhammad ibn Ja’far, who said: Narrated to us Shu’bah, from ‘Amr ibn Murrah, who said: I heard Salim ibn Abi al-Ja’d narrating from ‘Uwaym ibn Sa’idah, that the Prophet (ﷺ) said: "The martyrs of my nation are few. A man may be killed, and he is a martyr, and a man may die of a stomach ailment, and he is a martyr, and a man may die of the plague, and he is a martyr, and a man may die of drowning, and he is a martyr."