Imam Ali [a] said: “When our Qaim (12th Imam) rises, the sky will send down its drops, the earth will grow its plants, enmity will come out from the servants’ hearts, and savages and beasts will continue to live together peacefully”[i]

[i] Bihar-ul-Anwar, vol. 52, p. 316

The Holy Prophet [s] said: “The person who dies and has not known the Imam of his time has died the same as one who died during the Age of Ignorance.”[i]
(Sunni sources)

[i] Musnad-i-Ahmad-ibn-Hanbal, vol. 2, p. 83; vol. 3, p. 446 & vol. 4, p.   96: Sahih-i-Bukhari, vol. 5, p. 13 & Sahih-i-Muslim vol. 6, p. 21, No.1849. In addition to 25 other references introduced by Sunni scholars

The Holy Prophet [s] said: “Happiness is for the one who will attend the Qaim (12th Imam) of my Ahlul Bayt and will follow him before his rise. This person will love his (Qaim’s) lovers and hate his enemies, and will accept the leadership of the Imams from before his advent. These ones are my friends, and are the most sincere members of my Ummah (community) whom I honor very much.”[i]

[i] Bihar-ul-Anwar, vol. 52, p. 129