The Messenger of Allah ﷺ said regarding the urine of a nursing infant, "The urine of a baby boy is sprinkled with water, and the urine of a baby girl is washed."Qatada said, "This applies as long as they have not yet started eating solid food. Once they begin eating, both are washed alike."
حدثنا محمد بن بشار حدثنا معاذ بن هشام حدثني أبي عن قتادة عن أبي حرب بن أبي الأسود عن أبيه
أن رسول الله ﷺ قال في بول الغلام الرضيع ينضح بول الغلام ويغسل بول الجارية قال قتادة وهذا ما لم يطعما فإذا طعما غسلا جميعا
[Sahih]. Abu Dawud also narrated it in the Book of Purification, Chapter on the urine of a young boy touching clothing, no. 378, and Ibn Majah, no. 525, from the hadith of Muaz bin Hisham Dastawai, with the same wording. Ibn Khuzayma graded it sahih, no. 284, as did Ibn Hibban, no. 247, and Hakim, 1/165, and Dhahabi agreed with him. The hadith has very many corroborating narrations found in Abu Dawud (376) and elsewhere.