Musnad Abu Ya'la al-Mawsili 150:119

Bishr ibn al-Walid narrated to us, Sharik narrated to us, from Hisham ibn Urwah, from his father, from Aisha, she said: The Messenger of Allah, may Allah bless him and grant him peace, used to have young children brought to him, and he would supplicate for them and invoke blessings upon them. A young boy was brought to him, and he urinated on him. He then called for water and poured it over it.