إيمان
Īmān
Faith: belief in God, His angels, scriptures and messengers, the Last Day and the decree, which the Quran joins with righteous deeds.
What it means
“The righteous man is he who believes in God, the Last Day, the angels, the Book and the prophets” (2:177). The Quran adds works: “those who believe and do righteous deeds” appears dozens of times. It describes the believers as those whose hearts tremble when God is mentioned and whose faith grows when His verses are recited (8:2–4). It distinguishes outward submission (islām) from faith (īmān) in the heart (49:14).
What the sources say
The Quran asks Muslims to believe in all revelations: “we make no distinction between any of His messengers” (2:285). That includes the earlier scriptures, and the Quran tells the Prophet that if he doubts, he should ask those who have been reading the Book before him (10:94).
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 23, listed as ĪMĀN. The definition is restated here.