Al-Kāfi - The Book of Belief and Disbelief

5.Al-Husayn ibn Muhammad has narrated from Mu’alla ibn Muhammad and a number of our people from Ahmad ibn Muhammad all of them from al- Washsha’ from Aban from abu Basir who has said the following: “I heard Abu Ja’far (a.s.) saying, ‘The Arabs have said, “We have established belief.” Say, “You have not established belief but say, ‘We have accepted Islam.’ Belief has not yet entered your hearts.” (49:14) Whoever thinks that they (Arabs) had belief, his thoughts are false and whoever thinks that they had not accepted Islam he has lied.’” وثق كالصحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (7/126))