Years ago, when I frequented the city library for hours every day, I happened to come across a book on wisdom and sayings from the land that was once Persia. The organization of the book was along historical lines, and there were chapters for each period, first as one of the oldest historical civilizations, familiar to us through Gilgamesh and Hammurabi, then as the center of the Persian empire, intercoursing with Greeks, Macedonians, Jews, Indian civilizations, and Romans, then the Zoroastrian period, then the Islamic periods, and finally modern Iran and its neighbors -- each period with distinct wisdom and character. What stood out, though, was a chapter on honesty, which came from the Zoroastrian period, before Islam reached the region.
It seems from the literature -- the book I've since lost the name of, and which isn't available online anyway from search of the quotes I copied out at the time, as well as minor references in other historical sources -- the Persians had a special reputation for honesty, which extended from cultural to legal rules about their personal conduct even to their associations with others:
"To the men of other nations, it set forth the absolute fact that verity might be assumed when the Persian of all men spoke."
"The Persian who, without knowledge of the truth, or, in any event, without knowledge of the falsity of what he says, plainly it may be spoken, is a liar."
"He himself is a liar who is good to a liar, and he is a righteous man to whom the righteous man is dear; since thou, oh God, has created men's souls from the beginning."
"Let none of ye attend the liar's words and demands. He leads house, clan, district and country to misery and destruction. Resist them, then, with weapons."
"And the liar may be recognized as having shunned the man who has particular friendship with the truth. From this spirt have the liars fallen away, oh God, but never the righteous."
"In this faith of ours, oh God, the Right is laid down for blessings, to ruin against the heresy of the lie. Therefore I strive for the fellowship of the Good Mind and I forbid all intercourse with the liar."
"In the burden of the liar, and in the punishment set aside for him, it was necessary to apportion to him all the misconduct that the enemy of God would cherish."
"According as it is with the laws that govern this life, so shall the judge deal most justly toward the man of the lie and toward the man of the Right, toward him in whom the false and the true balance."
"The person who speaks falsely is found the most despicable and is first condemned. Later most other forms of sin."
"The sin of reliance on the false."
"The liar is condemned, is everywhere patent, and ever because he is the foe of truth."
"The duty commences when the light falls on the falsity and it appears. For clarity is sure to come and the falsehood is sure to be seen."
Of the man who has lived the virtuous life, and has encouraged others to do likewise, "Such a one shall there arrive as the strongest of the strong, who here below most powerfullly impelleth the righteous unto good works, to think perfect thoughts, speak perfect words and do perfect deeds."
"Virtue is his one permanent possession."
"When one shall do even that which he knows to be a sin, that is disobedience, and disobedience is the nature of the adversary."
"That the walks of men be directed three places: the abode of the well-informed, the abode of the good, and the abode of fire. The abode of the well-informed, that men become wiser and that religeon may find lodgement within him. The abode of the good, that between good and evil, he may eschew the evil and carry with him the good. The abode of fire, that the evil one may turn from him."
More information on the Persian concept of honesty isn't readily available. Anyone who has sources or particularly quotes from original material, visit the discussion.
Added, after a tip by jhaubrich11
In the 5th century BC, Herodotus also made a note about this aspect of Persian culture:
... Their sons are carefully instructed from their fifth to their twentieth year, in three things alone---to ride, to draw the bow, and to speak the truth. ...
They hold it unlawful to talk of anything which it is unlawful to do. The most disgraceful thing in the world, they think, is to tell a lie; the next worst, to owe a debt: because, among other reasons, the debtor is obliged to tell lies. ...