Ibn Abi al-Aswad (may Allah have mercy on him) narrates from his father that the Prophet (peace and blessings be upon him) said: "The urine of a baby boy is to be sprinkled, and the urine of a baby girl is to be washed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4161