What is the ruling on placing a marker on the grave of one of one's relatives so that he can identify it and visit it?

Question:
He says: Honorable Shaykh, may Allah grant you success. What is the ruling on placing a marker on the grave of one of one's relatives so that he can identify it, visit it, and make du'a' for him?

Answer:
There is no objection if it is not writing, not coloring with light or paint, and if it is merely a line or a stone placed on it, such that no one knows it except him. The Prophet (peace and blessings be upon him) placed a stone on the grave of Uthman ibn Maz'un in order to visit it (peace and blessings be upon him). So there is no harm in placing a stone on it, placing a stick, driving a stick into it, putting a line near it, or something similar to these markers that no one knows except him. Yes.