Abdur Rahman bin Mahdi عبد الرحمن بن مهدي · The Chapters on Jihad

“We hoped that when he died it would be as a martyr in the cause of Allah.” The Messenger of Allah (ﷺ) said: “In that case the martyrs of my nation would be few. Being killed in the cause of Allah is martyrdom; dying of the plague is martyrdom; when a pregnant woman dies in childbirth that is martyrdom; and dying of drowning, or burning, or of pleurisy, is martyrdom.”

It was narrated from Anas bin Malik that the Prophet (ﷺ) entered Makkah on the day of the Conquest, with a helmet on his head.