Ablutions (Wudu')
وَبِإِسْنَادِهِ قَالَ " لاَ يَبُولَنَّ أَحَدُكُمْ فِي الْمَاءِ الدَّائِمِ الَّذِي لاَ يَجْرِي، ثُمَّ يَغْتَسِلُ فِيهِ ".The same narrator said that the Prophet (ﷺ) had said: "You should not pass urine in stagnant water which is not flowing then (you may need to) wash in it
From Sahih al-Bukhari, whose reports the scholars accept as authentic.