I entered the mosque to offer the prayer and, when I went out, I did not find my shoes. They were worth 600 SAR. Then, I found them with another person. As I frankly accused him of having taken my shoes, he said that they belonged to his friend who lives in the same district in which I live and that they had exchanged their shoes. I was not convinced and I told him to immediately give me back my shoes. He did not agree and gathered his friends to quarrel with me. I told him that he had to bring my shoes back the next day. He said that he would do so. The next day, he said that his friend took back his shoes. I felt very angry because my shoes were so expensive. I made up my mind to take his shoes after performing the prayer at school. I conceived a plan and carried it out along with my friends, as a friend of mine took his shoes and gave them to me. For your knowledge, the shoes of that man are not worth more than 20 SAR. I have kept them until today. I consider it to be a part of the 600 SAR. Is this correct? Am I sinful?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

If something was stolen or usurped from someone and he found it with the one who stole it or someone else, then he has the right to take it back if he does not fear a greater evil than that of losing it, such as the attribution of betrayal and theft to him. It is not stipulated to refer that matter to a judge.

If one is not able to take his exact property and only takes part of the property of the one who usurped him, he is allowed to take it until he takes back his right from him in full.

Al-Bukhari said:

"Chapter of the retaliation of the oppressed person if he finds the property of the one who oppressed him. Ibn Seereen said: "He should retaliate," and he recited the saying of Allaah Almighty (which means): {And if you punish [an enemy, O believers], punish with an equivalent of that with which you were harmed.} [Quran 16: 12]"

Al-Haafith Ibn Hajar said:

"Does this means that he should take from him something that is equivalent to his property, even without a ruling issued by a judge? This is the issue known as ath-thafr (recovery of a stolen item of property). The compiler is inclined to adopt this opinion. Therefore, he quoted the report of Ibn Seereen, following his habit of overweighing opinions based on reports."

Accordingly, if you are certain that the shoes that you have found with that man are yours based on signs that indicate so, then there is nothing wrong with taking his shoes, considering them  part of the right he owes you.

Allaah Knows best.