(18) باب مَتَى يَصِحُّ سَمَاعُ الصَّغِيرِ
Narrated Mahmud bin Rabi`a:
When I was a boy of five, I remember, the Prophet (ﷺ) took water from a bucket (used for getting water out of a well) with his mouth and threw it on my face.
Reference: Sahih al-Bukhari 77
In-book reference: Book 3, Hadith 19
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 3, Hadith 77