It is not permissible for him to do that, because the money that he is taking, claiming that he is entitled to it, is something that his boss has entrusted him with, and the one who is entrusted with something is obliged to honour that trust and render it back to its owner. It is not permissible for him to betray him with regard to that.
Allaah says (interpretation of the meaning):
“Verily, Allaah commands that you should render back the trusts to those, to whom they are due”
And the Prophet (peace and blessings of Allaah be upon him) said: “Render back the trust to the one who entrusted it to you, and do not betray those who betray you.” Narrated by al-Tirmidhi, 1264; classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
The Prophet (peace and blessings of Allaah be upon him) enjoined rendering back trusts to those who entrusted them to you, and he forbade betraying the one who betrayed you.
The Standing Committee was asked about a man who works in a grocery store, and his boss only gives him his salary every four or six months. Is it permissible for him to take his monthly salary from the money of the grocery store in which he works without his boss’s knowledge?
It is not permissible for you to take your salary from the grocery store in which you work without your boss’s knowledge or permission. You have to ask your boss for your salary, and if he refuses then you should refer your complaint to the appropriate authorities so that they can make him pay you.
Fataawa al-Lajnah al-Daa’imah, 15/145
Shaykh al-Islam Ibn Taymiyah said in Majmoo’ al-Fataawa, 30/372:
If a man has a right due to him from another, can he take it or its equivalent without his permission? This falls into two categories:
1 – If the reason for his demanding his right is obvious and does not require proof, such as a woman’s right to maintenance from her husband, or the child’s right to maintenance from his father, or the guest’s right to hospitality from the people with whom he is staying, then in this case he has the right to take it without permission from the one who owes that to him without a doubt. It was proven in al-Saheehayn that Hind bint ‘Utbah ibn Rabee’ah said: “O Messenger of Allaah, Abu Sufyaan is a stingy man and he does not give me sufficient maintenance for myself and my child.” He said: “Take what is sufficient for you and your child, on a reasonable basis.” In this report the Prophet (S) permitted her to take her maintenance, on a reasonable basis, without asking the permission of the owner of the money. Similarly, if it is known that a person’s wealth has clearly been wrongfully seized and the people know about that, he may take the seized wealth or its equivalent from the one who seized it, and so on.
2 – If the reason for demanding his right is not obvious, such as when a person denies that he owes him money, or denies that he seized his wealth unlawfully, and the claimant has no proof. There are two scholarly views in this case. One is that he should not take it; this is the view of Maalik and Ahmad. The other is that he can take it; this is the view of al-Shaafa’i.
Those who say that he should not take it if he has no clear proof of his right quote as evidence the report narrated in al-Sunan from Abu Hurayrah, that the Prophet (peace and blessings of Allaah be upon him) said: “Render back the trust to the one who entrusted it to you, and do not betray those who betray you.” And in al-Musnad it is narrated that Basheer ibn al-Khasaasah said: “O Messenger of Allaah, we have neighbours who do not leave anything, great or small, but they take it. If we have the opportunity to take something from them, should we take it?” He said, “No. Render back the trust to the one who entrusted it to you, and do not betray those who betray you.”
These ahaadeeth explain that if the right of the one who is wronged is not obvious, and he takes it in a sneaky manner, he does not have the right to do that, even if all he intends is to take something equivalent to his right, but he does that by betraying someone who trusted him. That is because when he entrusted him with his wealth and he took some of it without his permission and there is no clear proof of his rights, then this is a betrayal of trust.
That is because betrayal in and of itself is haraam, so it should not be used as a means of taking one’s rights. Betrayal is akin to lying. If it is said that this is not a betrayal, rather it is taking one’s rights and the Prophet (peace and blessings of Allaah be upon him) only forbade betraying the one who betrays you, in the sense of taking more from his wealth than is your right – it should be noted that this argument is weak on a number of counts, one of which is that in the hadeeth it says, “we have neighbours who do not leave anything, great or small, but they take it. If we have the opportunity to take something from them, should we take it?” He said, “No. Render back the trust to the one who entrusted it to you, and do not betray those who betray you.” The second is that he said: “Do not betray those who betray you,” i.e., you should not respond to the one who betrays you by doing the same thing to him as he did to you. The third is that this action is undoubtedly a betrayal. Rather those who allowed it did so as a retaliatory measure, because there are cases in which retaliation is allowed, such as murder, banditry and seizing wealth unlawfully. And there are some cases in which retaliation is not allowed, such as immoral actions, lying, etc. When he said here, “Do not betray those who betray you,” it is known that this is a case in which it is not permitted to punish in like manner.