The Prophet ﷺ urinated and Umar was standing behind him with a jug of water. He said: What is this, Umar? He replied: Water for you to perform ablution with. He said: I have not been commanded to perform ablution every time I urinate. If I were to do so, it would become a sunnah. (Using translation from Abū Dāʾūd 42)
أَنَّ النَّبِيَّ ﷺ بَالَ فَأَتَاهُ عُمَرُ بِكُوزٍ مِنْ مَاءٍ فَقَالَ مَا هَذَا يَا عُمَرُ؟ قَالَ تَوَضَّأْ بِهِ قَالَ لَمْ أُومَرْ كُلَّمَا بُلْتُ أَنْ أَتَوَضَّأَ وَلَوْ فَعَلْتُ كَانَتْ سُنَّةً لَفْظُ حَدِيثِ فَهْدِ بْنِ حَيَّانَ