النهي عن البول في الماء الراكد
A direct prohibition on urinating into still, non-flowing water — an early public-health instruction protecting a shared water source from contamination.
لَا يَبُولَنَّ أَحَدُكُمْ فِي الْمَاءِ الدَّائِمِ الَّذِي لَا يَجْرِي، ثُمَّ يَغْتَسِلُ فِيهِ
“None of you should urinate in standing water that does not flow, and then bathe in it.” (meaning, not a literal translation)
The instruction specifically distinguishes standing from flowing water — the concern is contamination accumulating in a body of water with no current to disperse it, not a blanket rule about all water sources equally.
Grouped by commentators with the site's existing 'Covering Vessels & Tying Waterskins' entry as part of a broader set of Prophetic instructions protecting water sources from contamination before germ theory existed to explain why. Ibn al-Qayyim treats this as part of the same underlying concern seen across several hygiene entries: protecting a communal resource that many people would subsequently use.
Modern public health fully endorses this same principle — contaminating a standing water source used for bathing or drinking is a well-understood disease-transmission risk, addressed today through sanitation infrastructure rather than individual behavioral instruction alone.