One hundred and eighteen narratives have been handed down to us, which point that the Earth would never be without God’s proof.
Allame Majlesi collected these narratives in the chapter “Al-Iztirar Ela al-Hujjah” [Necessity of God’s proof] of Biḥār al-ʾAnwār
Also the late Kulayni has mentioned such narratives in the book “Kāfī”; the chapter “Kitab Al-Hujjah”. For example:

[This version of the document[of this narrative] is accurate and its narrators are reliable and trusted.]
Kulayni narrated from Muhamad bin Yahya, from Ahmad bin Muhamad, from Ali bin Hakam, from Rabee’ ibn Muhamad, from Abdullah bin Suleiman, from imam Sadiq (pbuh), that the imam stated,

“The God’s proof will continuously stay in the earth.”

From article of Ayatollah Asefi, “Intizar Mo’ud” Journal, No.5