It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Allah Almighty has certain servants whom He spares from being killed. He lengthens their lives in good deeds, makes their provision good, keeps them alive in well-being, and takes their souls in well-being upon their beds, and then grants them the ranks of the martyrs."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10333