It is narrated from Sayyiduna Salman (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whom do you count as a martyr among you?" The Companions said: The one who is killed in the path of Allah. He (peace and blessings be upon him) said: "Then the martyrs of my Ummah would be few. Being killed is martyrdom, plague is martyrdom, abdominal disease is martyrdom, and dying in childbirth is martyrdom."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6091