Is the head of Imam Hussein, may God be pleased with him, buried in Al-Hussein Mosque in Cairo? What is the ruling on praying there? And is seeking blessings from it considered polytheism?

Al-Husayn ibn Ali, may Allah be pleased with them both, was martyred in Iraq, and his head was transported to Medina and buried there. As for the claim that his head is buried in Egypt, it has no basis. Sheikh al-Islam Ibn Taymiyyah, Ibn Kathir, and other scholars and verifiers have denied this, affirming that what is in Egypt is a falsehood and does not contain the grave of Al-Husayn. Furthermore, Al-Husayn's body is unanimously agreed to be buried in Karbala.

As for visiting the alleged grave in Al-Husayn Mosque in Egypt, it is not permissible due to the presence of great transgressions such as prostration, circumambulation, and supplicating to other than Allah.

It is also not permissible to seek blessings by supplicating at the graves of prophets and righteous people, because visiting graves was legislated for admonition, reflection, and supplicating for the deceased, not for supplicating to them or seeking intercession through them.