Hadith: If anyone does not fight in the cause of Allah, equip a warrior in the cause of Allah, or stay behind to look after a warrior's family, Allah shall afflict him with a calamity before the Day of Judgment

عن أبي أمامة رضي الله عنه مرفوعاً: « مَنْ لَمْ يَغْزُ أَوْ يُجَهِّزْ غَازِيًا أَوْ يَخْلُفْ غَازِيًا في أهله بخير، أصابه الله بقارعة قبل يوم القيامة ».
[حسن] - [رواه أبو داود]

Abu Umāmah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "If anyone does not fight in the cause of Allah, equip a warrior in the cause of Allah, or stay behind to look after a warrior's family, Allah shall afflict him with a calamity before the Day of Judgment."
Hasan/Sound. - [Abu Dawood]

Explanation

This Hadīth urges Muslims to fight in the cause of Allah. It also stresses Allah's severe punishment in this world before the Hereafter inflicted on the one who abandons fighting in the cause of Allah, or abandons aiding the warriors fighting in the cause of Allah with his wealth, or abandons helping the warriors' families by looking after them in their absence. Anyone abandons these actions will suffer severe calamities for not supporting the religion of Allah properly.