“Whoever asks Allah sincerely for martyrdom [Allahumma inni as’aluk ash-shahadah], Allah will cause him to reach the status of the martyrs even if he dies in his bed.” [‘Sahih al-Bukhari’; # 1909]‘
[Al-`Adawee said it was sound, and that it was reported by by Muslim, page 55 of volume 13; Abu Dãwood, page 179 of volume 2; and Ibn Mãjah, #2797.]