Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
- There is nothing wrong with sprinkling water on graves, but it also has nothing to do with cooling the deceased.
- The actions that benefit the dead are: ongoing charity, beneficial knowledge (which he has left behind), or a righteous child who will pray for him.
In response to your question, the late Muslim scholar Sheikh Ibn `Uthaymeen (may Allah have mercy upon him), stated:
There is nothing wrong with sprinkling water on graves after burying a deceased person, because water holds the earth together in order not to scatter right and left.
With regard to what the common people believe that sprinkling water cools down the deceased, there is no basis for this.
As for what benefits the dead, Prophet Muhammad (peace be upon him) said, “When a person dies, all his deeds come to an end except three: ongoing charity, beneficial knowledge (which he has left behind), or a righteous child who will pray for him.” (An-Nasai’)
Allah Almighty knows best.
Source: www.islamqa.info