Firstly it is proven in the Hadith of Prophet Muhammad (peace be upon him) that he placed two twigs on the two graves that he was passing by to reduce their punishment.
The Prophet (peace and blessings of Allaah be upon him) passed by two graves and said: “They are being punished but they are not being punished for something that was difficult to avoid [?}.” Then he said, “One of them used to go about spreading malicious gossip, and the other used not to take precautions to avoid being contaminated with urine.” Then he took a fresh branch, broke it in two and planted each piece on a grave. Then he said: “May their punishment be reduced so long as this does not dry out.”
Narrated by al-Bukhaari, 1378; Muslim, 292.
This indicates that the punishment may be reduced, but what is the relationship between these two branches and the reduction of these punishments for these two persons?
It was said that the branches glorify Allah(by saying tasbeeh) as long as they do not dry out and that tasbeeh reduces the punishment of the deceased. Based on this people came to conclusion that it is Sunnah of Prophet Muhammad(peace be upon him) to place leaves on the graves to reduce the punishment of the deceased and also to recite the tasbeeh on the graves of the deceased to ease their punishment.
Some of the scholars said: This reason is da’eef (weak) because the two branches would recite tasbeeh whether they were fresh or dry, because Allaah says (interpretation of the meaning):
“The seven heavens and the earth and all that is therein, glorify Him and there is not a thing but glorifies His Praise. But you understand not their glorification”
Pebbles in the hands of the Messenger (peace and blessings of Allaah be upon him) were heard to recite tasbeeh even though pebbles are dry, so how are we to understand the hadeeth?
We may understand from this example that the Messenger of Allah(peace be upon him) hoped that Allah will ease their punishment for them as long as the twigs remain fresh and also to warn people against the actions that they used to do because their actions were serious as it says in the report that the Prophet (peace and blessings of Allaah be upon him) said, “But it is serious.”
One of them used to walk about spreading malicious gossip causing mischief among the slaves of Allah and stir up enmity and hatred among them.
The other did not take precautions to avoid being contaminated by urine, if he was not able to keep himself clean that means none of his prayers was valid and accepted and hence this is a serious matter.
This is the most likely understanding of the meaning of the hadeeth, that it was a temporary intercession and a warning to the ummah, not because the Messenger (peace and blessings of Allaah be upon him) wanted to offer ongoing intercession.
Some scholars – may Allaah forgive them – say that it is Sunnah to place a fresh branch, etc on the grave so that the punishment might be reduced. But this understanding is very far-fetched, and it is not permissible for us to do that for several reasons.
we do not know if a person in the grave is being punished or not. We cannot be sure and thinking in such terms about them is as if we are disrespecting and mistreating them.
We do not know just like Prophet Muhammad (peace be upon him) who is being punished or not. He had a revelation from Allah about those graves.
It may be that he is being blessed, or it may be that this deceased person is one of those whom Allaah blessed with forgiveness before he died because of one of the many things that bring forgiveness, so he died having been forgiven by the Lord of all people, in which case he would not deserve to be punished.
None of the salaf performed this action or testify of doing so. This action was not part of their way and they were the most knowledgeable of people about the sharee’ah of Allaah.