(2) باب أَيْنَ فُرِضَتِ الصَّلاَةُ .
It was narrated from Anas bin Malik that the prayers were enjoined in Makkah, and that two angels came to the Messenger of Allah (ﷺ) and took him to Zamzam, where they split open his stomach and took out his innards in a basin of gold, and washed them with Zamzam water, then they filled his heart with wisdom and knowledge.
Reference: Sunan an-Nasa'i 452
In-book reference: Book 5, Hadith 5
English translation: Vol. 1, Book 5, Hadith 453