Praise be to Allah.
Undoubtedly this is a reprehensible and offensive action that violates the sanctity of the dead. The grave of a dead person is like the house of a living person. The Prophet (peace and blessings of Allaah be upon him) drew attention to the repulsive nature of this action when he said: “If I were to walk on live coals or a sword, or repair my shoes using my own feet, this would be better for me than walking on the grave of a Muslim. There is no difference between answering the call of nature in the middle of a graveyard or in the middle of the marketplace.” (Ibn Maajah). In al-Zawaa’id it says that its isnaad is saheeh, and in Irwa’ al-Ghaleel (63) it is classed as Saheeh. “Or repair my shoes using my own feet” – this is something that is extremely difficult and if it were possible it would be very painful indeed, but despite all that it is still preferable to walking on the grave of a Muslim. “There is no difference between answering the call of nature in the middle of a graveyard or in the middle of the marketplace” – means that both actions are equally repulsive, and whoever does one will not refrain from doing the other.
And Allaah knows best.