The prayers were made obligatory in Mecca. Two angels came to the Messenger of Allah ﷺ and took him to Zamzam, where they opened his chest and removed its contents into a golden basin. They washed it with Zamzam water, then filled his chest with wisdom and knowledge.
أخبرنا سليمان بن داود عن ابن وهب قال أخبرني عمرو بن الحارث أن عبد ربه بن سعيد حدثه أن البناني حدثه
أن الصلوات فرضت بمكة وأن ملكين أتيا رسول الله ﷺ فذهبا به إلى زمزم فشقا بطنه وأخرجا حشوه في طست من ذهب فغسلاه بماء زمزم ثم كبسا جوفه حكمة وعلما
No references are available.
[Its chain of transmission is sahih] It is found in Kubra, no. 316.