I want to go to Hajj but I took some money from someone without his knowledge and I can't give it back to him. What shall I do to keep Haram money from me?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If you have enough money that could cover all expenses of Hajj, then you should hasten to perform it.

On the other hand, your committing a sin or earning some Haram money does not give you a right to delay performing Hajj.  But if you do not have sufficient means to perform Hajj, you should not perform it using other people’s money.

You may put the illicit money apart until you get the opportunity to return it to its owner.  In fact, this money is due on you as it belongs to another person and you are held responsible for it until you return it to its owner.  The Prophet (Sallallahu Alaihi wa Sallam) said: The hand which takes is responsible till it pays. (Reported by Imam Ahmad and In Sunan)

Allah knows best.