Usul al-Kafi
Book 4: The Book of Divine Proof

Chapter 50
A legacy from Prophet
397. 1. Imam Musa al-Kazim (p): The extent of our knowledge has three dimensions: the knowledge of the past, the knowledge of the events that have taken place and will take place, and the knowledge of the events that are occurring now, which are put in our hearts and conveyed to us through our ears.
398. 2. Imam Jafar as-Sadiq (p) was asked by Harith Ibn al-Mugheera: Tell me about the knowledge of the erudite (the Imams (p)).
The Imam (p): It is a legacy from the Prophet Muhammad (p) and Imam Ali (p).
Harith: In our conversation, we say that knowledge is inspired in your hearts and whispered in your ears.
The Imam (p): Yes, in this way as well.