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

Chapter 69
Imamate of Imam Muhammad al-Baqir (p): the fifth Imam

429. 2. Isa Ibn Abdullah cites from his grandfather When Imam Zainul Abideen (p) was near his death, and his sons were gathered around him, he drew his attention to Imam Muhammad al-Baqir (p) and said: O Muhammad, take this box to your house. Verily, there are no Dinars or Dirhams in it, but it is filled with knowledge.