What is the liability of the speculator (Mudarib) who exceeds his authorized actions or purchases something forbidden?

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The speculator is liable for the capital loss if he acts beyond his authority or buys something he was forbidden to purchase, according to the opinion of the majority of scholars. This view is reported from Abu Hurairah, Hakim ibn Hizam, Abu Qilabah, Nafi', Iyas, Al-Sha'bi, Al-Nakha'i, Al-Hakam, Hammad, Malik, Al-Shafi'i, Ishaq, and the Ahlu al-Ra'y (People of Opinion). The basis for this ruling is that the speculator is managing the property of another without permission, thus incurring liability like a usurper (ghasib).