Ruling on relieving oneself in graveyards

This message came from Hamud ibn Hadram al-Harbi. He says: I am presenting a question to your eminence, hoping from Allah, then from your eminence, that you would graciously provide me with information. May Allah reward you with good:
One day, I went to the village of al-Hanakiyyah with one of my friends to take care of some necessary business. When we arrived at al-Hanakiyyah, my friend went into the house of one of his relatives, and I remained outside the house to wait for him. During that time, I went to an open piece of land near the aforementioned house to relieve myself. When I sat down to relieve myself, one of the children shouted at me that this place is a graveyard, and that it is not permissible to relieve oneself in graveyards. It is known that there are no clear signs indicating that it is a graveyard, and I had not known about it before. Please inform me whether I have committed a sin for this or not. May Allah reward you with good, and guide you to what is good in this world and the Hereafter. Peace be upon you, and Allah’s mercy and blessings.
Answer: One does not relieve oneself in graves. The Prophet (peace and blessings be upon him) said: , so one does not sit on them, neither to relieve oneself nor for any other reason. Rather, they are to be respected. A Muslim respects the living and the dead alike. Therefore, it is not permissible for anyone to relieve himself in graves, whether by urinating or defecating. Nor is it permissible for him to step on a grave or sit on it; rather, he must be careful to avoid doing so. However, the one who relieved himself in a piece of land without knowing that it was a graveyard has committed no sin, as long as he did not know and was not aware that it was a graveyard. There is no sin on him until he learns that it is a graveyard. Yes.