عَنْ سَهْلِ بْنِ مُعَاذٍ عَنْ أَبِيهِ رَضِيَ اللَّهُ عَنْهُ عَنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ أَنَّهُ قَالَ مَنْ حَرَسَ مِنْ وَرَاءِ الْمُسْلِمِينَ فِي سَبِيلِ اللَّهِ تَبَارَكَ وَتَعَالَى مُتَطَوِّعًا لَا يَأْخُذُهُ سُلْطَانٌ لَمْ يَرَ النَّارَ بِعَيْنَيْهِ إِلَّا تَحِلَّةَ الْقَسَمِ فَإِنَّ اللَّهَ تَبَارَكَ وَتَعَالَى يَقُولُ {وَإِنْ مِنْكُمْ إِلَّا وَارِدُهَا} [مريم: 71]
It is narrated from Sayyiduna Mu'adh (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Whoever keeps watch in the path of Allah to protect the Muslims, and his action is voluntary, not due to compulsion from the ruler, then he will not see the Fire with his own eyes, except to fulfill the oath, because Allah the Exalted has said: And there is none among you but will pass over it (the Fire).