First of all, we would like to stress that the urine of male babies who are completely breast-fed is overlooked and pardoned. It is sufficient just to sprinkle water over the place of urine.
In his book Fiqh As-Sunnah, the late Azharite scholar Sheikh Sayyed Sabiq (may Allah rest his soul in peace) states the following:
“The urine of an unweaned male baby [i.e. one who is exclusively breast-fed] is overlooked and pardoned. It is sufficient just to sprinkle water over the urine of a nursing male baby. This is based on the Hadith of Umm Qais who came to the Messenger of Allah with her nursing son. After a while, the baby urinated in the Prophet’s lap. The Prophet (peace and blessings be upon him) called for some water, which he sprinkled over his clothes, and did not give them a complete washing. (Reported by Al-Bukhari and Muslim)
`Ali (may Allah be pleased with him) reported that the Messenger of Allah said, “The urine of a baby boy should have water sprinkled upon it. The urine of a baby girl is to be washed off.” Says Qatadah, “This refers to a male baby that has not yet begun to eat. If he already eats, then the garment is to be washed.”
This hadith is reported by Ahmad, Abu Dawud, at-Tirmidhi and Ibn Majah. In al-Fath, Ibn Hajr says its chain is sahih (authentic).
Sprinkling is sufficient as long as the boy is only nursing. If he eats solid food, his urine must be washed from the clothes and body. There is no disagreement on this latter point. Perhaps the reason for this exemption to the male baby’s urine is that people have a tendency to carry their male babies around, and it would have been difficult to clean the clothes after their frequent urinations.”