Truth stands for the conformity between word and deed. It plays a great role in the lives of both the individuals and communities. Truth is the beauty of speech and ground of success. From this cause, the Islamic Sharia, ( 1 ) in both the Quran and Sunna, ( 2 ) glorified and urged telling truth:
“Those who have brought the truth and those who have acknowledged it are those who have fear of Allah. They will receive whatever they want from their Lord. Thus is the reward of the righteous ones. (39:33-4)"
“Allah will say, “This is the Day when the truthful ones will benefit from their truthfulness. (5:119)"
“Believers! Have fear of Allah and always be friends with the truthful ones. (9:119)"
The Prophet (s) said: “Truth is the adornment of speech."
Imam as-Sadiq (a) said: “Do not be deceived by their very much offering of prayers and observance of fasting. In fact, prayers and fasting have become habits that they feel desolate if they omit them. You should test them by their truthfulness and fulfil lment of trusts."
“The deeds of the truthful are growing."
This means that the deeds of the truthful are ongoing and their rewards are, too, growing. Thus, God accepts only the deeds of the pious ones. Truth, then, is one of the most significant characteristics of piety.
source : http://www.maaref-foundation.com