I clearly remember a mouthful of water that the Messenger of Allah ﷺ spat from a bucket in our home. In another narration he added, "And I was five years old at the time."
إني لأعقل مجة مجها رسول الله ﷺ من دلو في دارنا. وزاد في رواية: وأنا ابن خمس سنين.
Bukhari related it in "The Chapter on Softening the Heart" (6422), and Muslim in "The Chapter on Mosques" (33:265), both through routes from Zuhri, from Mahmud bin Rabi, who said, and then he mentioned it.As for the other narration, Bukhari related it in "The Chapter on Knowledge" (77) through the route of Zubaydi, from Zuhri, with the same wording.