Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: Once the Messenger of Allah (peace and blessings be upon him) was lying on his back in one of his houses when Sayyiduna Hasan came crawling until he sat on the chest of the Prophet (peace and blessings be upon him), then he urinated on his chest. I came to remove him, and the Messenger of Allah (peace and blessings be upon him) woke up and said: "Woe to you, O Anas! Leave my son, the fruit of my heart. Whoever hurts him has hurt me, and whoever hurts me has hurt Allah." Then the Messenger of Allah (peace and blessings be upon him) called for water and poured it over the urine, and said: "Water is poured over the urine of a boy, and the urine of a girl is washed."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2614