Assalamu'alaykum. I would like to resend this because the fatwa referred hasn't answered my question which focuses on the assumption of what she is liable for. A girl used to take money with force from another children. She only remembers that she took these money during the 3rd grade of her elementary school. She doesn't remember how much money she took from them daily. And now that she has repented, she wanted to return the money. But when she summed the total money that could cover a whole year of the money she took daily, the amount was too great, she doesn't think she took that much. So she assumed she only took these money during several months and she is counting only what she is certain she is liable for (the minimum amount of money). Can she use that assumption?
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
She has to estimate the amount she had taken unlawfully, in a way she believes she would cover what she took, and then she should return it to the owners. She must pay back enough not have any doubt that she still needs to pay anything extra.
Ibn Al-'Arabi said in his Tafseer (interpretation of the Quran): "If a person is confused about how much is lawful from how much is forbidden, then he should estimate the amount that he considers to be forbidden, and he should take precautions about this to the extent that he should not have any doubt that he had paid off what he owes, and that he is acquitted from sin." [End of quote]
Allah knows best.
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