Sahih Muslim 1915 a
It has been narrated on the authority of Abu Huraira (through another chain of transmitters) that the Messenger of Allah (ﷺ) said:
Whom do you consider to be a martyr among you? They (the Companions) said: Messenger, of Allah, one who is slain in the way of Allah is a martyr. He said: Then (if this is the definition of a martyr) the martyrs of my Umma will be small in number. They asked: Messenger of Allah, who are they? He said: One who is slain in the way of Allah is a martyr; one who dies in the way of Allah, is a martyr; one who dies of plague is a martyr; one who dies of cholera is a martyr. 
Ibn Miqsam said: I testify the truth of your father's statement (with regard to this tradition) that the Prophet (ﷺ) said: One who is drowned is a martyr.
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا جَرِيرٌ، عَنْ سُهَيْلٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ
 قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ مَا تَعُدُّونَ الشَّهِيدَ فِيكُمْ ‏"‏ ‏.‏ قَالُوا يَا رَسُولَ اللَّهِ
 مَنْ قُتِلَ فِي سَبِيلِ اللَّهِ فَهُوَ شَهِيدٌ قَالَ ‏"‏ إِنَّ شُهَدَاءَ أُمَّتِي إِذًا لَقَلِيلٌ ‏"‏ ‏.‏ قَالُوا فَمَنْ هُمْ
 يَا رَسُولَ اللَّهِ قَالَ ‏"‏ مَنْ قُتِلَ فِي سَبِيلِ اللَّهِ فَهُوَ شَهِيدٌ وَمَنْ مَاتَ فِي سَبِيلِ اللَّهِ فَهُوَ شَهِيدٌ
 وَمَنْ مَاتَ فِي الطَّاعُونِ فَهُوَ شَهِيدٌ وَمَنْ مَاتَ فِي الْبَطْنِ فَهُوَ شَهِيدٌ ‏"‏ ‏.‏ قَالَ ابْنُ مِقْسَمٍ
 أَشْهَدُ عَلَى أَبِيكَ فِي هَذَا الْحَدِيثِ أَنَّهُ قَالَ ‏"‏ وَالْغَرِيقُ شَهِيدٌ ‏"‏ ‏.‏