"O Messenger of Allah, why will the believers be tested in their graves except the martyr?" He said: "The flashing of the swords above his head is trial enough."  

عَنْ رَجُلٍ مِنْ أَصْحَابِ النَّبِيِّ ﷺ أَنَّ رَجُلاً قَالَ يَا رَسُولَ اللَّهِ مَا بَالُ الْمُؤْمِنِينَ يُفْتَنُونَ فِي قُبُورِهِمْ إِلاَّ الشَّهِيدَ قَالَ كَفَى بِبَارِقَةِ السُّيُوفِ عَلَى رَأْسِهِ فِتْنَةً  

"The plague, abdominal illness, drowning and dying in childbirth are martyrdom." (One of the narrators) said: Abu 'Uthman narrated this to us several times, and on one occasion he attributed it to the Prophet.  

الطَّاعُونُ وَالْمَبْطُونُ وَالْغَرِيقُ وَالنُّفَسَاءُ شَهَادَةٌ قَالَ وَحَدَّثَنَا أَبُو عُثْمَانَ مِرَارًا وَرَفَعَهُ مَرَّةً إِلَى النَّبِيِّ ﷺ