Authentic Supplication Number 136.

The Prophet  said "Whoever asks Allah martyrdom truthfully, Allah would deliver him to the places of the martyrs. Even if he were to die upon his bed.

Reporters.
'Al-`Adawee said it was sound, and that it was reported by by Muslim, page 55 of volume 13; Abu Dawood, page 179 of volume 2; and Ibn Majah, #2797.