(Al-Anfal) 8 : 16
وَمَنْ يُوَلِّهِمْ يَوْمَئِذٍ دُبُرَهُ إِلَّا مُتَحَرِّفًا لِقِتَالٍ أَوْ مُتَحَيِّزًا إِلَىٰ فِئَةٍ فَقَدْ بَاءَ بِغَضَبٍ مِنَ اللَّهِ وَمَأْوَاهُ جَهَنَّمُ ۖ وَبِئْسَ الْمَصِيرُ
Anyone who turns back on such a day, except as a strategy of battle or to retreat to another group, then verily the wrath from Lord is upon him; and his abode is the Hell, and what an evil returning place!
To run away from the battlefield is considered as one of the heinous sins near Lord Allah as explained in verse 4: 31. Today, there is no killing and war. Instead, there is only Jihad against the hypocrites and their Mushrik followers with Adhikr—the Strong Weapon— as explained in verse 9: 73. See explanation 1: 7; 4: 150-151 and 22: 78.