The Messenger of Allah ﷺ urinated, and Umar stood behind him with a jug of water.The Prophet ﷺ asked, "What is this, Umar?"Umar replied, "Water for you to perform ablution with, Messenger of Allah."He said, "I have not been commanded to perform ablution every time I urinate. Had I done so, it would have become a sunnah."
حدثنا عفان قال حدثني عبد الله بن يحيى الضبي قال حدثني عبد الله بن أبي مليكة عن أمه
أن رسول الله ﷺ بال فقام عمر خلفه بكوز فقال ما هذا يا عمر قال ماء توضأ به يا رسول الله قال ما أمرت كلما بلت أن أتوضأ ولو فعلت ذلك كانت سنة
Its isnad is daif, not free from weakness. It contains Abdullah bin Yahya Dhabbi, and the mother of Ibn Abu Mulayka.If we say that Abdullah bin Yahya Dhabbi is not Thaqafi the twin, then they have remained silent about him, and Ibn Hibban rated him trustworthy, but many of them said he is Thaqafi, and Thaqafi is daif. If he is Dhabbi, his hadith is hasan.The mother of Ibn Abu Mulayka is unknown, I have not seen anyone mention her, and Haythami said the same, 1/241.The hadith was narrated by Ibn Majah, 1/118, no. 327, and Abu Dawud, 1/11, no. 42, and Ibn Abu Shayba, 1/54, all of them in the chapter on purification.