Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said: "The urine of a baby girl should be washed, and the urine of a baby boy should be sprinkled, as long as he has not started eating food."
Abu Isa (al-Tirmidhi) said: I asked al-Bukhari about this hadith, and he said: Sa'id bin Abi Arubah does not narrate it as marfu' (from the Prophet), while Hisham al-Dastuwa'i narrates it as marfu', and he is a hafiz. However, others besides Mu'adh bin Hisham narrated it from Hisham as mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4160