How is Muharram celebrated by Shia?
Why do Shia pray on stone?
Following instruction from the Qur’an, the Shia Imam Ja'far al-Sadiq stated that "prostration must be performed on pure earth or what grows on it, provided that it is not eaten or worn." (like leaves, wood, stone/marble so on). For example, prostration on paper is permissible because it is made of natural elements grown on earth.