Muwatta Malik, Book 2, Hadith 111 (USC-MSA) ⓘ

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "An infant boy was brought to the Messenger of Allah, may Allah bless him and grant him peace, and it urinated on him. The Messenger of Allah, may Allah bless him and grant him peace, called for some water and rubbed over the urine with it."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَنَّهَا قَالَتْ أُتِيَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِصَبِيٍّ فَبَالَ عَلَى ثَوْبِهِ فَدَعَا رَسُولُ اللَّهِ صلى الله عليه وسلم بِمَاءٍ فَأَتْبَعَهُ إِيَّاهُ ‏.‏