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Why is it compulsory to prostrate on the clay from Karbala?
It is not ! But the Shi'ah prefer to prostrate on the earth of Karbala because of the importance given to it by the Prophet (s) and the Imams from his Family (Ahl al-Bayt). After the martyrdom of Imam Husayn (a), his son Imam Zayn al-'Abidin (a) picked some up, declared it to be sacred dust, and kept it in a bag. The Imams (a) used to perform prostrations on it and make a tasbih out of it, and recited Allah's praises on it.
[Ibn Shahrashub, al-Manaqib, vol. 2, p. 251]
They also encouraged the Shi'ah to perform prostrations on them, with the understanding that it was not compulsory, but with a view to achieving greater recompense. The Imams (a) insisted that prostration before Allah must be on clean earth only and that it was preferable if it was performed on that earth of Karbala.
[al-Tusi, Misbah al-Mutahajjad, p. 511]
[al-Saduq, Man la yahduruhu'l faqih, vol. 1, p. 174]
The Shi'ah for a long time have kept this earth with them. Then, fearing that it might be desecrated, they kneaded it into small tablets or pieces, which are now called mohr or Turbah. During prayers we prostrate on it not as a compulsory act but in view of its special nature. Otherwise, when we have no pure soil with us, we prostrate on clean earth, or something that originates from it.
It is a pity that some people maliciously insist that the Shi'ah worship stones or that they worship Husayn (a). The truth is that we worship Allah alone by prostrating on the Turbah, not to it. And we never worship Imam Husayn, Imam Ali, or the Prophet Muhammad (s). We worship only Allah, and it is in accordance with Allah's order that we perform prostration only on pure earth.
Conclusion:
This is the reason why Shi'ah Muslims carry small tablets, usually made from the earth of Karbala, which enables them to do prostration on this highly recommended object and to follow the sunnah of the Prophet (s).
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