Sayyiduna Abu Layla (may Allah be pleased with him) narrates: We were with the Prophet (peace and blessings be upon him) when Sayyiduna Hasan (may Allah be pleased with him) came crawling until he climbed onto his chest and urinated on him. We rushed to take him, but the Prophet (peace and blessings be upon him) said: "My son, my son." Then he called for water and poured it over it.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6394