It is narrated from Sayyiduna Safwan bin Umayyah (may Allah be pleased with him), attributing it to the Prophet (peace and blessings be upon him), that he (peace and blessings be upon him) said: "Plague, death in childbirth (nifas) and drowning are martyrdom."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7298