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)
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.