Sahih Muslim Book - 33, Hadith - 4940

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، قَالَ : قَرَأْتُ عَلَى مَالِكٍ ، عَنْ سُمَيٍّ ، عَنْ أَبِي صَالِحٍ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّ رَسُولَ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ، قَالَ : بَيْنَمَا رَجُلٌ يَمْشِي بِطَرِيقٍ ، وَجَدَ غُصْنَ شَوْكٍ عَلَى الطَّرِيقِ فَأَخَّرَهُ ، فَشَكَرَ اللَّهُ لَهُ ، فَغَفَرَ لَهُ. وَقَالَ : الشُّهَدَاءُ خَمْسَةٌ : الْمَطْعُونُ ، وَالْمَبْطُونُ ، وَالْغَرِقُ ، وَصَاحِبُ الْهَدْمِ ، وَالشَّهِيدُ فِي سَبِيلِ اللهِ عَزَّ وَجَلَّ.

It was narrated from Abu Hurairah that the Messenger of Allah (s.a.w) said: "While a man was walking on the road, he found a thorny branch on the road, so he removed it. Allah appreciated that and forgave him." And he said: "The martyrs are five: The one who dies of the plague, the one who dies of a stomach disease, the one who drowns, the one who is crushed beneath a falling wall, and the martyr who is killed in the cause of Allah (glorified and exalted is He)."