Sahih Al Bukhari – Book of Beginning Of Creation

Volumn 004, Book 054, Hadith Number 538.
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Narated By Abu Huraira : Allah's Apostle said, "A prostitute was forgiven by Allah, because, passing by a panting dog near a well and seeing that the dog was about to die of thirst, she took off her shoe, and tying it with her head-cover she drew out some water for it. So, Allah forgave her because of that."