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.'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 526 (IT)
Arabic reference (IT): Book 1, Hadith 569 (IT)