It was narrated from Anas that a Bedouin urinated in the Masjid, and some of the people went after him, but the Messenger of Allah (ﷺ) said:
"Leave him and do not restrain him." When he had finished he called for a bucket (of water) and poured it over it. [1]Abu 'Abdur-Rahman (An-Nasa'i) said: "Meaning: 'Do not interrupt him.'"[1]The author will cite this narration again in No. 330 as a possible proof for setting the minimum, since it mentions "a bucket" as if this is the minium amount required.
Arabic/English book reference: Vol. 1, Book 1, Hadith 53