It is narrated from Sayyiduna Safwan bin Umayyah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Plague, drowning, burning and death in childbirth (nifas) are martyrdom for my Ummah."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7299