Sudair relates from Imam Jafar Sadiq (a.s.): There is an occultation for our Qaim, which will be prolonged. I asked: Why, O son of Allah’s Messenger? He replied: Because Allah wants the practices (Sunnah) of His Prophets in their occultation should also occur on him. And O Sudair, his occultation must come to an end.

Allah says: That you shall most certainly enter one state after another. (Surah Inshiqaq (84):19)
It means: The Sunnah of those who have gone before you.
Behaar al-Anwaar v 51 p 142