الكافي 2/1/59/5

5. A number of our people have narrated from Ahmad ibn Muhammad ibn Khalid from ibn Faddal from al-‘Ala’ ibn Razin from Muhammad ibn Muslim who has said the following: “I heard abu Ja’far عليه السلام saying, ‘Once an angel came to the Messenger of Allah and said, ‘‘Allah, the Most Majestic, the Most Holy, gives you the choice to be a servant and a humble messenger, or to be an angel and a messenger.” He looked to Jibril who made a gesture with his hand to be humble. He (the Messenger of Allah) said, “I want to be a humble servant and a messenger.” The messenger (the angel) said, “Despite this, there is no reduction in what is with your Lord.” The Imam said, “With him were the keys to the treasures of earth.’””