Arabic text
عَن سَهْلِ بْنِ حُنَيْفٍ رضي الله عنه أَنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ: «مَنْ سَأَلَ اللهَ الشَّهَادَةَ بِصِدْقٍ بَلَّغَهُ اللهُ مَنَازِلَ الشُّهَدَاءِ، وَإِنْ مَاتَ عَلَى فِرَاشِهِ».
Translation
Sahl ibn Hunayf (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) said: "Whoever sincerely asks Allah for martyrdom, Allah will make him reach the status of martyrs even if he dies on his bed."
Explanation
The Prophet (may Allah's peace and blessings be upon him) informs that whoever seeks martyrdom and death in the cause of Allah and is sincere and faithful in his intention to Allah Almighty, Allah will give him the ranks of martyrs by his sincere intention, even if he dies in bed, not in Jihad.
Source: HadeethEnc.com