Hadithcore
Mishkat al-Masabih, 3808

Sahl b. Hunaif reported God’s Messenger as saying, “If anyone asks God for martyrdom with a genuine purpose God will bring him to the dwellings of the martyrs, even if he dies on his bed.” Muslim transmitted it.

وَعَن سهل بن حنيف قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: " مَنْ سَأَلَ اللَّهَ الشَّهَادَةَ بِصِدْقٍ بَلَّغَهُ اللَّهُ مَنَازِلَ الشُّهَدَاءِ وَإِنْ مَاتَ عَلَى فِرَاشِهِ. رَوَاهُ مُسلم

References1 variant
In-Book Reference
Book 19, Hadith 22