Imam al-Shafi'i (may Allah have mercy on him) says: A fine is not to be doubled on anyone for anything; punishment is upon bodies, not upon property. We abandoned doubling the fine only because the Messenger of Allah (peace and blessings be upon him) ruled, concerning the damage done by the she-camel of al-Bara bin Azib (may Allah be pleased with him), that "guarding by day is the responsibility of the owners of property, and whatever livestock damage by night is the liability of their owners." He said: So they are liable for it at its value, not at twice its value. And the claimant's word is not accepted regarding the amount of the value, because the Prophet (peace and blessings be upon him) said: "Proof is upon the claimant, and the oath is upon the one against whom the claim is made."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السرقة / 17288