Usul al-Kafi
Book 5:
The Book of Belief and Disbelief

Chapter 100
Paucity of believers

1064. 5. Imam Musa al-Kazim (p): By God, there was an era when there was only one worshipper of God on the earth. Had there been any one else with him, God would have mentioned him in the verse: Prophet Abraham (Ibrahim) (p) was an Ummat (a model, a community by himself), devoutly obedient to God, upright and he was not of the polytheists (Q, 16:120). God dealt with that era as He pleased and then added Prophet Ishmael (Ismael) (p) and Prophet Isaac (Ishaq) (p) and they became three. By God, the believers are in a minority and the unbelievers are in a majority … (B5,C100,T5)