Sunan Ibn Majah, Book 1, Hadith 569 (In-Book) ⓘ
Abu Samh said: "I was a servant of the Prophet, and Hasan and Husain was brought to him and (the infant) urinated on his chest. They wanted to wash it, but the Messenger of Allah said: 'Sprinkle water on it, for the urine of a girl should be washed, but the urine of a boy should be sprinkled over with water.'"
حَدَّثَنَا عَمْرُو بْنُ عَلِيٍّ، وَمُجَاهِدُ بْنُ مُوسَى، وَالْعَبَّاسُ بْنُ عَبْدِ الْعَظِيمِ، قَالُوا حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا يَحْيَى بْنُ الْوَلِيدِ، حَدَّثَنَا مُحِلُّ بْنُ خَلِيفَةَ، أَخْبَرَنَا أَبُو السَّمْحِ، قَالَ كُنْتُ خَادِمَ النَّبِيِّ ـ صلى الله عليه وسلم ـ فَجِيءَ بِالْحَسَنِ أَوِ الْحُسَيْنِ فَبَالَ عَلَى صَدْرِهِ فَأَرَادُوا أَنْ يَغْسِلُوهُ فَقَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " رُشَّهُ فَإِنَّهُ يُغْسَلُ بَوْلُ الْجَارِيَةِ وَيُرَشُّ عَلَى بَوْلِ الْغُلاَمِ " .
also referenced under: Hadith 526 (Reference) & Volume 1, Book 1, Hadith 526 (DarusSalam)