A loan from somebody else

Q: I sold a car to someone in installments. After he had paid some of the installments, I told him that I was forgiving the rest of the money that he owed me and I signed a waiver in front of a judge in the court. However, the next day I regretted having forgiven him the rest of the payments and he continued to pay the installments. Are these payments Halal (lawful) or Haram (prohibited)? Should I return the money that he has paid of these installments, (Part No. 13; Page No. 177) as I only want what is Halal? Please advise me and may Allah reward you with the best.

A: If the matter is as you mentioned, you have no right to take the money that you forgave from the indebted person.