The great sage and scholar of Islam, Ibn al-Qayyim, said: “Truthfulness is the greatest of stations, from it sprout all the various stations of those traversing the path to God; and from it sprouts the upright path which if not trodden, perdition is that person’s fate. Through it is the hypocrite distinguished from the believer and the inhabitant of Paradise from the denizen of Hell. It is the sword of God in His earth: it is not placed on anything except that it cuts it; it does not face falsehood expect that it hunts it and vanquishes it; whoever fights with it will not be defeated; and whoever speaks it, his word will be made supreme over his opponent. It is the very essence of deeds and the well spring of spiritual states, it allows the person to embark boldly into dangerous situations, and it is the door through which one enters the presence of the One possessing Majesty. It is the foundation of the building of Islam, the central pillar of the edifice of certainty and the next level in ranking after the level of prophethood.”
By practicing truthfulness, a person betters himself, his life is made upright and due to it, he is elevated to praiseworthy heights and raised in ranks in the sight of God as well as the people. As the Prophet Muhammad, may the mercy and blessings of God be upon him, related:
“I order you to be truthful, for indeed truthfulness leads to righteousness, and indeed righteousness leads to Paradise. A man continues to be truthful and strives for truthfulness until he is written as a truthful person with God. And beware of falsehood, for indeed falsehood leads to sinning, and indeed sinning leads to the Fire. A man continues to tell lies and strives upon falsehood until he is written as a liar with God.” (Saheeh Muslim)
So, truthfulness is something which is to be cultivated till it becomes implanted in a person’s soul and disposition and therefore reflected throughout the person’s character. Ali b. Abi Talib, the cousin and son-in-law of the Prophet Muhammad, mentioned the positive reciprocal effect of behaving truthfully with people in this worldly life:
“Whoever does three things with regards to people, they will necessitate three things from him: whenever he speaks to them he is truthful; whenever they entrust him with something he does not betray them; and whenever he promises them something he fulfils it. If he does this, their hearts will love him; their tongues will praise him; and they will come to his aid.”
As for the Next Life, through God’s Grace and Mercy, the obedient ones - practitioners of truthfulness - will reach a station in Paradise alongside those most fortunate of souls mentioned in the revelation.
“And whosoever obeys God and His Messenger, such will be in the company of those whom God has blessed: the Prophets, the truthful ones, the martyrs, and the righteous. And how excellent a company are such people!” (Quran 4:69)
In fact, truthfulness is an essential attribute of every single prophet who graced the earth. We are told in the Quran:
“And mention in the Book, Abraham: surely he was a most truthful Prophet.” (Quran 19:41)
“And mention in the Book, Ishmael: surely, he was a man true to his word, and he was a Messenger, a Prophet.” (Quran 19:54)
“And mention in the Book, Enoch: surely he was a most truthful Prophet.” (Quran 19:56)
We also read in the Quran how a man incarcerated alongside the Prophet Joseph addressed him with the words:
“Joseph! O most truthful one!...” (Quran 12:46)
…and that Mary, the mother of Jesus, was also declared truthful in the Words of God:
“The Messiah (Jesus), son of Mary, was no more than a Messenger; many were the Messengers that passed away before him. His mother (Mary) was a truthful one, a Believer….” (Quran 5:75)
… and the Companions of God’s Messenger, the “believers” mentioned time and time again in the Quran, also reached the lofty ranks of the truthful ones:
“The believers are but those people who believed in God and His Messenger without ever feeling doubt thereafter, and strove with their souls and possessions in the way of God; those are the ones who are the truthful.” (Quran 49:15)
Hence, to tread the path of truthfulness is to tread the path of the most righteous of God’s creation. And as for ways and means to engender this most noble of virtues into our daily lives, then we have been left an ocean of teachings from God’s Final Messenger to humanity, the Prophet Muhammad, detailing and describing precisely what the virtue, nay!, the injunction of truthfulness requires. One from among these vast and numerous sayings of God’s Messenger is his plea:
“Guarantee for me six things and I will guarantee Paradise for you: tell the truth when you speak, fulfill your promises, be faithful when you are trusted, safeguard your private parts, lower your gaze, and withhold your hands (from harming others).”
And God confirmed the truthfulness of these words of His Beloved Messenger with His Own True Word:
“For Muslim men and women, for believing men and women, for devout men and women, for truthful men and women, for patient men and women, for humble men and women, for charitable men and women, for fasting men and women, for men and women who guard their chastity, and for men and women who engage much in God’s praise: for them has God prepared forgiveness and a great reward.” (Quran 33:35)
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by expert : 1] Madarij as-Salikeen.
 Ibn Muflih, Adaab ash-Shari’a.
 Reported by Ubaadah, in As-Saheehah.