سنن ابن ماجہ #525

Water should be sprinkled over the urine of a boy, and the urine of a girl should be washed." Abul-Hasan bin Salamah said: "Ahmad bin Musa bin Ma'qil narrated to us that Abul-Yaman Al-Misri said: 'I asked Shafi'i about the Hadith of the Prophet, "Water should be sprinkled over the urine of a baby boy, and the urine of a baby girl should be washed," when the two types of water (urine) are the same. He said, "This is because the urine of the boy is of water and clay, but the urine of the girl is of flesh and blood." Then he said to me: "Did you understand?" I said: "No." He said: "When Allah the Most High created Adam, He created Eve (Hawwa') from his short rib, so the boy's urine is from water and clay, and the girl's urine is from flesh and blood." Then he said to me: "Did you understand?" I said: "Yes." He said: "May Allah cause you benefit from this