Sahih Bukhari Volume 4, Book 59, Hadith 3322

حَدَّثَنَا الْحَسَنُ بْنُ الصَّبَّاحِ، حَدَّثَنَا إِسْحَاقُ الأَزْرَقُ، حَدَّثَنَا عَوْفٌ، عَنِ الْحَسَنِ، وَابْنِ، سِيرِينَ عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ غُفِرَ لاِمْرَأَةٍ مُومِسَةٍ مَرَّتْ بِكَلْبٍ عَلَى رَأْسِ رَكِيٍّ يَلْهَثُ، قَالَ كَادَ يَقْتُلُهُ الْعَطَشُ، فَنَزَعَتْ خُفَّهَا، فَأَوْثَقَتْهُ بِخِمَارِهَا، فَنَزَعَتْ لَهُ مِنَ الْمَاءِ، فَغُفِرَ لَهَا بِذَلِكَ ‏"‏‏

Narrated 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."