Explanation of Riyaadh Saliheen The Chapter On Truthfulness By Abu Zakariya Yahya bin Sharaf An-Nawawi

Truthfulness means: conformity of reports to reality. If you were to report something and it is consistent with reality, then it is classified as a true report (e.g. today is Sunday, and it is Sunday). But if you said: today is Monday while it is not then this is a false report. Therefore, a report is classified as true if it matches reality; otherwise, it is false. 

Truthfulness covers both sayings and actions. The latter is achieved when the individual's heart is an image of the outside appearance. The individual who shows off, for example, is not truthful because he displays a state of obedience while he is not, the polytheist is not truthful because he exhibits himself as a monotheist, but he is not, the hypocrite is not truthful because he pretends to be a believer but he is not, and the innovator is not truthful because he claims to be following the Prophet (sallallahu alayhi wa sallam) but he is not.

 However, truthfulness is achieved when the report and reality are identical. It is a characteristic of the believers; as opposed to lying, which is a characteristic of hypocrites- we seek Allah’s refuge from it. Allah says, “O you who believe! Be afraid of Allah, and be with those who are true (in words and deeds).” [Soorah at-Tawbah 9:119]