Quran 9:120

مَا ڪَانَ لِأَهۡلِ ٱلۡمَدِينَةِ وَمَنۡ حَوۡلَهُم مِّنَ ٱلۡأَعۡرَابِ أَن يَتَخَلَّفُواْ عَن رَّسُولِ ٱللهِ وَلَا يَرۡغَبُواْ بِأَنفُسِہِمۡ عَن نَّفۡسِهِۦ‌ۚ ذَٲلِكَ بِأَنَّهُمۡ لَا يُصِيبُهُمۡ ظَمَأٌ۬ وَلَا نَصَبٌ۬ وَلَا مَخۡمَصَةٌ۬ فِى سَبِيلِ ٱللهِ وَلَا يَطَـُٔونَ مَوۡطِئً۬ا يَغِيظُ ٱلۡڪُفَّارَ وَلَا يَنَالُونَ مِنۡ عَدُوٍّ۬ نَّيۡلاً إِلَّا كُتِبَ لَهُم بِهِۦ عَمَلٌ۬ صَـٰلِحٌ‌ۚ إِنَّ ٱللَّهَ لَا يُضِيعُ أَجۡرَ ٱلۡمُحۡسِنِينَ ١٢٠

Neither the dwellers of the city, nor the Arabs around them, shall seek to stay behind the messenger of ALLAH (when he mobilizes for war). Nor shall they give priority to their own affairs over supporting him. This is because they do not suffer any thirst, or any effort, or hunger in the cause of ALLAH, or take a single step that enrages the disbelievers, or inflict any hardship upon the enemy, without having it written down for them as a credit. ALLAH never fails to recompense those who work righteousness.