It is narrated from Hazrat Aisha (may Allah be pleased with her) that people used to bring their children to the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) would pray for them. Once, a child was brought and he urinated on the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) said, "Pour water over it."
Hadith Referenceمسند احمد / مسند النساء / 24192
Hadith Gradingحکم دارالسلام:حديث صحيح من فعله صلى الله عليه وسلم كما فى البخاري، 222، ومسلم: 286