Where is al-Husayn buried, and how important is it to know where the graves of the Sahaabah are?
Question

                A questioner says that people talk a great deal and have different opinions about where the grave of al-Husayn is located. Can the Muslims benefit from knowing exactly where it is?.
Praise be to Allah.In fact people differed concerning that. It 
    was said that he is buried in Syria, or in Iraq, and Allaah knows best what is true. With regard to his head, they also differed concerning that; 
    it was said that it is buried in Syria, or in Iraq, or in Egypt. The correct view is that the site in Egypt is not his grave, rather that is a 
    mistake and the head of al-Husayn is not there. A number of scholars have written essays on that and explained that there is no evidence for the 
    head of al-Husayn being in Egypt. The most likely to be correct is the view that it is in Syria, because it was taken to Yazeed ibn Mu’aawiyah who 
    was in Syria. There is no basis for the view that it was taken to Egypt. Either it was kept in Syria or it was returned to his body in Iraq. 
Whatever the case, the people do not need to 
    know where it is buried or where it is. Rather what is prescribed is to pray for forgiveness and mercy for him, may Allaah forgive him and be 
    pleased with him, for he was killed unlawfully. So we should pray for forgiveness and mercy for him, and hope for much good for him. He and his 
    brother al-Hasan will be the leaders of the youth of Paradise, as the Prophet  (peace and blessings of Allaah be upon him) said. May Allaah be 
    pleased with them. 
If a person’s grave is known, there is 
    nothing wrong with saying salaams to him and making du’aa’ for him, as other graves may be visited, without going to extremes in that or 
    worshipping them. It is not permissible to ask the dead to intercede, because nothing can be asked of the dead; rather we should make du’aa’ for 
    them and pray for mercy for them if they were Muslims, because the Prophet  (peace and blessings of Allaah be upon him) said: “Visit the 
    graves, for they will remind you of the Hereafter.” 
If a person visits the graves of al-Husayn or 
    al-Hasan or any other Muslim to make du’aa’ for them and pray for mercy and forgiveness for them, as he would do at the grave of any other Muslim, 
    this is Sunnah. But visiting graves to pray to their occupants or seek their help or ask them to intercede – this is a reprehensible action, and 
    indeed it is major shirk. It is not permissible to build mosques or domes etc over graves, because the Messenger  (peace and blessings of 
    Allaah be upon him) said: “May Allaah curse the Jews and Christians, for they took the graves of their Prophets as places of worship.” (Saheeh – 
    agreed upon). And because it was narrated from Jaabir (may Allaah be pleased with him) in al-Saheeh that the Prophet  (peace and 
    blessings of Allaah be upon him) forbade plastering over graves, sitting on them and erecting structures over them.” So t is not permissible to 
    plaster over graves, perfume them, place screens around them or erect structures over them; all of that is forbidden and these are means that lead 
    to shirk. And we should not pray at graves because the Prophet  (peace and blessings of Allaah be upon him) said: “Those who came before you 
    used to take the graves of their Prophets and righteous people as places of worship; do not take graves as places of worship, for I forbid you to 
    do that.” (Narrated by Muslim in his Saheeh from Jundub ibn ‘Abd-Allaah al-Bajali (may Allaah be pleased with him). 
This hadeeth indicates that it is not 
    permissible to pray at graves or to take them as mosques; and because that is a means that leads to shirk and worshipping someone other than 
    Allaah by calling upon them (the occupants of the graves), seeking their help, making vows to them, and touching the graves to seek their 
    blessings. Hence the Prophet  (peace and blessings of Allaah be upon him) warned against that. Rather graves should be visited in the manner 
    prescribed in sharee’ah only, to give salaams to them and make du’aa’ for them and pray for mercy for them, but without travelling specifically 
    for that purpose. 
And Allaah is the Source of strength and the 
    Guide to the straight path.