In our view, urine is treated like blood. As long as it does not exceed the size of a dirham, there is no harm in it.
حدثنا محمد بن مقاتل حدثنا ابن المبارك أخبرنا مسعر
البول عندنا بمنزلة الدم ما لم يكن قدر الدرهم فلا بأس به
No references are available.
Its isnad is sahih. Muhammad bin Muqatil is trustworthy and a hafiz, and his hadith appears in Bukhari. This hadith is the evidence relied upon by the jurists in determining the amount of impurity that is excused.