Source text
وَلَا تَنْجُسُ الْبِئْرُ بِالْبَعْرِ وَالرَّوْثِ وَالْخِثْيِ إِلَّا أَنْ يَسْتَكْثِرَهُ النَّاظِرُ أَوْ أَنْ لَا يَخْلُوَ دَلْوٌ عَنْ بَعْرَةٍ
• A small amount of the listed animal droppings is excused in the well.
• It is treated as excessive if an observer regards it as a large amount, or if the drawn buckets are repeatedly not free from a dropping.
• This exception is specific to the type of droppings discussed here; it should not be generalized to every kind of impurity.