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

Chapter 68
Imamate of Imam Zainul Abideen (p): the fourth Imam

428. 4. Fulayh Ibn Abi Bakr ash-Shaybani says that once he was in a session with Imam Zainul Abideen (p) and his son Imam Muhammad al-Baqir (p) was with him when Jabir Ibn Abdullah al-Ansari came to him, and greeted him. Then, Jabir took the hand of Imam Muhammad al-Baqir (p) and moved away with him. Then, he said to Imam Muhammad al-Baqir (p): Prophet Muhammad (p) informed me that I would (live to) see a man from his Ahlul Bayt, who would be called Imam Muhammad Ibn Ali, and whose patronymic (Kunyah) would be Abu Jafar. The Prophet (p) told me to convey his blessing to him, when I see him (p).
Jabir went away, and Imam Muhammad al-Baqir (p) conveyed this to his father Imam Zainul Abideen (p).
Imam Zainul Abideen (p): O my dear son, may you be pleased with the fact that God has chosen you as my successor. Do not let your brothers know about this, lest they conspire against you, as the brothers of Prophet Yusuf (Joseph) (p) did against him.