An Arabi came and urinated in the mosque. The Messenger of Allah ﷺ said, "Pour a bucket or a large pail of water over it."
حدثنا سفيان عن يحيى
جاء أعرابي فبال في المسجد فقال رسول الله ﷺ أهريقوا عليه ذنوبا أو سجلا من ماء
Its isnad is sahih. Yahya is Ibn Saeed Ansari. The hadith was narrated by Bukhari 1/322 no. 219 in Fath al-Bari, in the chapter on wudu, "The Prophet ﷺ left the Bedouin alone until he finished urinating," and by Muslim 1/236 no. 284, in the chapter on purification, on the obligation of washing away urine. Also by Abu Dawud 1/103 no. 380, and Tirmidhi 1/276 no. 148, who said, hasan sahih.