“Truthfulness leads to Al-birr (righteousness) and al-Birr (righteousness) leads to paradise, a man keeps on telling the truth until he becomes known as a truthful person. Falsehood leads to Al-Fujur (wickedness-evil-doing), and al-Fujur leads to the hell fire, a man keeps on telling lies until he is written as a liar before Allah.”
(Sahih Al-Bukhari)
Allaah says (interpretation of the meaning):
“O you who believe! Be afraid of Allaah, and be with those who are true (in word and deeds).” [al-Tawbah 9:119]
Ibn Katheer (may Allaah have mercy on him) said (2/414): “It means: be truthful and adhere to truthfulness, and you will be among its people and will be saved from calamity, and this will make a way out for you from your problems.”
Al-Hasan ibn ‘Ali ibn Abi Taalib (may Allaah be pleased with them both) said: “I memorized from the Messenger of Allaah (peace and blessings of Allaah be upon him): ‘Leave that which makes you doubt for that which does not make you doubt, for truthfulness is certainty and tranquillity, whilst lying is doubt and confusion.” (Reported by al-Tirmidhi, 2520; al-Nisaa’i, 8/327; and Ahmad, 1/200)