Ali reported that the Prophet ﷺ placed an infant on his lap to perform tahnik on him, and the child urinated on him. He called for water and poured it over the spot.
Azami 14088
Sahih
عن عائشة
أن النبي ﷺ وضع صبيا في حجره يحنكه، فبال عليه، فدعا بماء، فأتبعه.
Bukhari narrated it in Al-Adab (6002), and Muslim in Al-Tahara (286), both through routes from Hisham bin Urwa, from his father, from Ayesha, who narrated it as mentioned. The wording given is Bukhari's.