Musnad Ahmad 5:2

'Abd al-Samad ibn 'Abd al-Warith narrated to us, Hisham narrated to us, from Qatadah, from Abu Harb ibn Abi al-Aswad, from his father, from 'Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The urine of a male infant is to be sprinkled upon, and the urine of a female infant is to be washed." Qatadah said: "This is as long as they have not yet eaten food; but if they have eaten food, the urine of both of them is to be washed."