إحسان
Iḥsān
Excellence in faith and conduct: to worship God as though you see Him.
What it means
In the hadith of Gabriel, the Prophet defines iḥsān as worshipping God as though you see Him, for if you do not see Him, He sees you (Sahih al-Bukhari and Sahih Muslim). The Quran says God commands justice and ihsan (16:90), and asks: “Is the reward for ihsan anything but ihsan?” (55:60).
Often misunderstood as
That Islam is mostly rules and legal duties.
What the sources say
The hadith of Gabriel sets out three levels: islām, the acts of worship; īmān, belief; and iḥsān, the inward excellence behind both. The long tradition of Muslim spiritual writing, from al-Ghazali to Rumi, grew around this third level.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 29, listed as IḤSĀN. The definition is restated here.