In the name of Allah, the Gracious, the Merciful
It is not permissible for a Muslim to fight in jihad with the intention of receiving spoils from the enemy.
Allah said:
يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا ضَرَبْتُمْ فِي سَبِيلِ اللَّهِ فَتَبَيَّنُوا وَلَا تَقُولُوا لِمَنْ أَلْقَىٰ إِلَيْكُمُ السَّلَامَ لَسْتَ مُؤْمِنًا تَبْتَغُونَ عَرَضَ الْحَيَاةِ الدُّنْيَا
O you who believe, when you go forth in the cause of Allah, then investigate. Do not say to one who gives you a greeting of peace that he is not a believer, thereby seeking the goods of worldly life.
Surah An-Nisa 4:94
Rather, a Muslim may only fight with the intention of protecting the religion of Islam or defending the rights of innocent people.
Abu Musa reported: A man came to the Prophet, peace and blessings be upon him, and said, “O Messenger of Allah, who is fighting in the cause of Allah? Some of us fight out of anger and others out of zeal.” The Prophet raised his head and he said:
مَنْ قَاتَلَ لِتَكُونَ كَلِمَةُ اللَّهِ هِيَ الْعُلْيَا فَهُوَ فِي سَبِيلِ اللَّهِ عَزَّ وَجَلَّ
He who fights so that the word of Allah is made high is fighting in the cause of Allah the Exalted.
Source: Sahih Bukhari 123, Grade: Sahih
Theft from the battlefield is a major sin. A man in the time of the Prophet went to the Hellfire because he had stolen a cloak from the enemy.
Umar ibn Al-Khattab reported: On the day of Khaybar, some of the companions of the Messenger of Allah, peace and blessings be upon him, came and were saying, “So-and-so is a martyr. So-and-so is a martyr.” Then they passed by a man and they said, “So-and-so is a martyr.” The Messenger of Allah said:
كَلَّا إِنِّي رَأَيْتُهُ فِي النَّارِ فِي بُرْدَةٍ غَلَّهَا أَوْ عَبَاءَةٍ
He is certainly not, for verily, I saw him in the Hellfire because of a cloak he had stolen.
Source: Sahih Muslim 114, Grade: Sahih
In fact, a Muslim who fights with the intention of receiving spoils from the enemy in addition to serving the cause of Allah will receive no reward from Allah. Rather, a Muslim may only have a single intention to implement justice for the sake of Allah.
Abu Huraira reported: A man said, “O Messenger of Allah, a man intends to fight for the sake of Allah and he is seeking worldly gains.” The Messenger of Allah, peace and blessings be upon him, said:
لَا أَجْرَ لَهُ
There is no reward for him.
The people found that very difficult and they said, “Return to the Messenger of Allah, for perhaps he did not understand you.” The man returned and he said, “O Messenger of Allah, a man intends to fight for the sake of Allah and he is seeking worldly gain.” The Messenger of Allah said:
لَا أَجْرَ لَهُ
There is no reward for him.
Then he returned a third time and the Messenger of Allah said:
لَا أَجْرَ لَهُ
There is no reward for him.
Source: Musnad Ahmad 7840, Grade: Sahih
Nevertheless, the acquisition of spoils is an inevitable result of war. In the time of the Prophet, the spoils were given to the Prophet and he distributed them in charity.
Allah said:
يَسْأَلُونَكَ عَنِ الْأَنفَالِ قُلِ الْأَنفَالُ لِلَّهِ وَالرَّسُولِ
They ask you about the spoils of war. Say: The spoils are for Allah and the Messenger.
Surah Al-Anfal 8:1
The commander of the Muslim army should distribute the spoils of war as charity to those in need or to those who took part in the battle. A soldier who participates in the battle may be given some of the spoils as a payment for his service.
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
وَتَوَكَّلَ اللَّهُ لِلْمُجَاهِدِ فِي سَبِيلِهِ بِأَنْ يَتَوَفَّاهُ أَنْ يُدْخِلَهُ الْجَنَّةَ أَوْ يَرْجِعَهُ سَالِمًا مَعَ أَجْرٍ أَوْ غَنِيمَةٍ
Allah guarantees that one who strives in His cause will enter Paradise if he dies, or he will return home safely with a reward or spoils.
Source: Sahih Bukhari 2635, Grade: Sahih
This is an incidental benefit meant to alleviate the burden of those who are sacrificing their lives to defend others, but it must never be an objective in itself.
Success comes from Allah, and Allah knows best.