Praise be to Allaah.
The command to wage jihad for the sake of Allaah, and the warning against neglecting jihad, appear in many verses of the Qur’aan and ahaadeeth.
If the Muslims neglect jihad for the sake of Allaah, and prefer a life of ease, and focus only on this world, they will face humiliation and scorn, and all their affairs will be corrupted. They expose themselves to the wrath and anger of Allaah, and they expose Islam to loss and defeat at the hands of kufr. Hence neglecting jihad is a major sin.
Ibn Hajar said in al-Zawaajir:
The 390th, 391st and 392nd major sins are neglecting jihad when it becomes an obligation, which is when aggressors enter the Muslim land or when they seize a Muslim, and it is possible to rescue him from them and the people neglect jihad altogether and when the people in a region neglect to fortify their borders so that there is a risk of the kuffaar overrunning them because of that.” end quote.
Hence it was well known and well established among the Sahaabah that no one refrains from taking part in jihad when it becomes fard ‘ayn (an individual obligation) except one who is weak and is therefore excused or one who is a hypocrite. This is what was narrated by Ka’b ibn Maalik (may Allaah be pleased with him) when he stayed behind from the campaign of Tabook: “When I came out to the people after the Messenger of Allaah (peace and blessings of Allaah be upon him) had gone out, I went around among them and was distressed to see no one except a man who was known to be a hypocrite or weak men whom Allaah had excused.” Narrated by al-Bukhaari, 4066; Muslim, 4973.
The evidence also states some of the punishments that result from that. For example:
1 – Neglecting jihad leads to doom in this world and in the Hereafter.
In this world the craven coward is humiliated and enslaved, he is a follower, not a leader. In the Hereafter, neglecting jihad will be a cause of Allaah's punishment.
Allaah says (interpretation of the meaning):
“And spend in the Cause of Allaah (i.e. Jihad of all kinds) and do not throw yourselves into destruction (by not spending your wealth in the Cause of Allaah), and do good. Truly, Allaah loves Al-Muhsinoon (the good-doers”
[al-Baqarah 2:195]
al-Tirmidhi (2972) narrated that Aslam Abu ‘Imraan said: We were in the city of the Byzantines (i.e., Constantinople) and a great troop of the Byzantines came out to us. One of the Muslim men attacked the Byzantine ranks until he penetrated them, and the people shouted and said “Subhaan-Allaah, he has thrown himself into destruction.” Abu Ayyoob al-Ansaari stood up and said: “O people, you misinterpret this verse in this way; rather this verse was revealed concerning us, the Ansaar. When Allaah caused Islam to prevail and its supporters increased, we said to one another in secret, without speaking to the Messenger of Allaah (peace and blessings of Allaah be upon him): ‘Our wealth is neglected. Allaah has caused Islam to prevail and its supporters have increased. Why don’t we stay with our property and improve it?’ Then Allaah revealed Qur’aan to His Prophet (peace and blessings of Allaah be upon him), refuting what we had said: “And spend in the Cause of Allaah (i.e. Jihad of all kinds) and do not throw yourselves into destruction” [al-Baqarah 2:195]. This destruction was our staying with our property to improve it, and neglecting to fight (in jihad). Abu Ayyoob never stopped fighting for the sake of Allaah until he was buried in Constantinople. Classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
It says in Tuhfat al-Ahwadhi:
This hadeeth indicates that what is meant by throwing oneself into destruction is taking care of one’s family and wealth at the expense of jihad.
2 – Neglecting jihad is a cause of humiliation and scorn
Abu Dawood (3462) narrated that Ibn ‘Umar said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: “When you engage in ‘aynah transactions (a kind of transaction intended to circumvent the prohibition on riba or usury), and you take hold of the tails of oxen and you are content with agriculture (at the time when jihad is obligatory), and you give up jihad, then Allaah will send upon you humiliation that will not be dispelled until you return to your religion, Allaah will send upon you humiliation that will not be dispelled until you return to your religion, Allaah will send upon you humiliation that will not be dispelled until you return to your religion.” Classed as saheeh by al-Albaani in Saheeh Abi Dawood.
Our Messenger (peace and blessings of Allaah be upon him) indeed spoke the truth, for the one who looks at the state of the Muslims today will see that they have become very careless about their religion. They consume riba and they are focused on this world, and they have neglected jihad for the sake of Allaah. And what is the result? Allaah has subjected them to humiliation, and they turn to the east and to the west, humiliated and lowly, asking them for support against their enemies, and they do not realize [?] that this humiliation will not be lifted from them until they go back to their religion as the truthful Messenger (peace and blessings of Allaah be upon him) said.
Allaah has indeed spoken the truth:
“Give to the hypocrites the tidings that there is for them a painful torment.
Those who take disbelievers for Awliyaa’ (protectors or helpers or friends) instead of believers, do they seek honour, power and glory with them? Verily, then to Allaah belongs all honour, power and glory”
[al-Nisa’ 4:138-139 – interpretation of the meaning]
3 – Neglecting jihad is a cause of Allaah's punishment in this world and in the Hereafter
Abu Dawood (2503) narrated from Abu Umaamah that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever does not fight or does not equip a warrior or support the family of a warrior in his absence, Allaah will strike him with calamity before the Day of Resurrection.” Classed as hasan by al-Albaani in Saheeh Abi Dawood.
Al-Qaari’ah (translated here as calamity) means a disaster that occurs suddenly.