Musnad Abu Ya'la al-Mawsili 3:47

Ubayd Allah narrated to us, Mu'adh ibn Hisham narrated to us, my father narrated to me, from Qatadah, from Abu Harb ibn Abi al-Aswad al-Dili, from Abu al-Aswad, from Ali ibn Abi Talib, that the Prophet of Allah (may Allah bless him and grant him peace) said regarding the infant: "The urine of a boy is sprinkled [with water], and the urine of a girl is washed." Qatadah said: "This is as long as they have not yet eaten food. If they have eaten food, both are washed."