Abu Dawud Book 1, Hadith Number 379.

Chapter : How to clean the clothe smeared with the urine of a child.

Narated By Umm Salamah, Ummul Mu’minin : Al-Hasan reported on the authority of his mother that she was Umm Salamah pouring water on the urine of the male child until the age when he did not eat food. When he began to eat food, she would wash (his urine). And she would wash the urine of the female child.