Musnad Ahmad 1168:1

Sufyan ibn 'Uyaynah narrated to us, from al-Zuhri, from 'Ubayd Allah, from Umm Qays bint Mihsan, who said: "I entered upon the Prophet, peace and blessings of Allah be upon him, with a son of mine who had not yet eaten food, and he urinated on him. So he called for water and sprinkled it over it."