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 رَسُولَ اللهِ ﷺ بَالَ فَقَامَ عُمَرُ خَلْفَهُ بِكُوزٍ فَقَالَ مَا هَذَا يَا عُمَرُ؟ قَالَ مَاءٌ تَوَضَّأْ بِهِ يَا رَسُولَ اللهِ قَالَ مَا أُمِرْتُ كُلَّمَا بُلْتُ أَنْ أَتَوَضَّأَ وَلَوْ فَعَلْتُ ذَلِكَ كَانَتْ سُنَّةً