Sayyidah Aishah (may Allah be pleased with her) narrates: The Prophet (peace and blessings be upon him) urinated, and Sayyiduna Umar (may Allah be pleased with him) stood behind him (peace and blessings be upon him) with a vessel of water. The Prophet (peace and blessings be upon him) asked: O Umar, what is this? He replied: O Messenger of Allah, this is water so that you may perform ablution with it. The Prophet (peace and blessings be upon him) said: I have not been commanded to perform ablution every time I urinate; if I were to do so, it would become a Sunnah.
Ahmad recorded it, which Ibn Abi Mulaykah narrated from his mother, and I have not seen anyone who gave an account of her. Abu Ya'la recorded it from Ibn Abi Mulaykah, from his father, from Sayyidah Aishah (may Allah be pleased with her).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1244