Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 378
Narated By Ali b. Abi Talib : The Prophet (pbuh) said: He narrated the tradition to the same effect, but he did not mention the words "until the age of eating." This version adds: Qatadah said: This is valid until the time they do not eat food; when they begin to eat, their urine should be washed.