The Prophet ﷺ came to a refuse heap of some people and urinated while standing. I brought him water for ablution and started to step back from him, but he called me over until I was right behind him at his heels. He then performed ablution and wiped over his leather socks.
حدثنا هناد حدثنا وكيع عن الأعمش عن أبي وائل
أن النبي ﷺ أتى سباطة قوم فبال عليها قائما فأتيته بوضوء فذهبت لأتأخر عنه فدعاني حتى كنت عند عقبيه فتوضأ ومسح على خفيه
Sourcing, agreed upon by Bukhari and Muslim. Bukhari narrated it in the book of wudu, chapter on urinating while standing and sitting, no. 224, and Muslim in the book of purification, chapter on wiping over the socks, no. 273, from the hadith of Amash with the same wording. The hadith of Hammad from Sulayman [narrated by Ahmad, 4/246], and the hadith of Asim bin Bahdala [narrated by Ibn Majah, no. 306, and its chain is hasan].