It is reported in a tradition “May Allaah Have mercy upon (the dweller of) a grave that is unknown!” Is it permissible for me to place a sign on the grave of my relative therewith to distinguish it from among others whenever I visit it to receive a reward, derive lessons and supplicate to a good effect for him? I commit no violations neither wailing nor any religious innovation. I just pay visits according to the Sunnah. Is it permissible for me to make a sign, say a stone or its like, on the grave to distinguish it from others?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
There is no harm to place a stone or such on a grave as a sign by which its dweller is recognized. This is the opinion of the majority of Maaliki, Hanbali and Shaafi‘i jurists. Ash-Shaafi‘i himself stated that it is an act of Sunnah. When ‘Uthmaan ibn Math‘oon died, the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, ordered a man to bring a rock and, when he failed to carry it, the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, stood toward it, rolled up the sleeves of his cloak and brought it himself, placed it by his head and said: “I will know by it the grave of my brother and bury beside him those who will die of my family.” [Abu Daawood; Al-Albaani: Hasan] Abu Daawood narrated it under a chapter on gathering more than one body in a single grave on which a sign is placed in order to recognize it.
In his commentary, Shaykh ‘Abd-Al-Muhsin Al-‘Abbaad said in his Sharh Sunan Abi Daawood: “That is, to place a sign on the grave in order to know that it is the grave of so and so. This is reported in the Sunnah from the Messenger of Allaah, sallallaahu ‘alayhi wa sallam.”
As for the tradition mentioned by the generous asker: “May Allaah Have mercy upon (the dweller of) a grave that is unknown!” we did not find it in any of our references nor do we think its attribution to the Prophet, sallallaahu ‘alayhi wa sallam, is authentic.
Allaah Knows best.
You can search for fatwa through many choices