Sunan Ibn Majah 525 — Concerning the urine of an infant boy who is not

´It was narrated from 'Ali that :` The Prophet said concerning the urine of a nursing infant: "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."

Abu al-Yaman al-Misri says: I asked Imam Shafi’i about the hadith of the Prophet (peace and blessings be upon him) «يرش من الغلام ، ويغسل من بول الجارية» “Sprinkle water over the urine of a boy, and wash the urine of a girl”—what is the reason for the difference between the two, when both are equal in being urine? Imam Shafi’i replied: The urine of a boy is from water and clay, and the urine of a girl is from flesh and blood. Then he said to me: Do you understand? I replied: No. He said: When Allah the Exalted created Adam (peace be upon him), Hawwa was created from his small rib, so the boy’s urine is from water and clay, and the girl’s urine is from blood and flesh. Then he asked me: Do you understand? I said: Yes. Upon this, he said to me: May Allah the Exalted benefit you with this knowledge.