Satya

Satya (Sanskrit: सत्य; IAST: "satya)" is a Sanskrit word loosely translated as truth, essence. It also refers to a virtue in Indian religions, referring to being truthful in one's thought, speech and action. In Yoga, "satya" is one of five yamas, the virtuous restraint from falsehood and distortion of reality in one's expressions and actions. "(lit.) "oath""
Etymology.
In the Vedas and later sutras, the meaning of the word satya () evolves into an ethical concept about truthfulness and is considered an important virtue. It means being true and consistent with reality in one's thought, speech and action.
A related concept, sattva, also derived from "sat", means true essence, nature, spiritual essence, character. Sattva is also a guṇa, a psychology concept particularly in the Samkhya school of philosophy, where it means goodness, purity, clean, positive, one that advances good true nature of self.
Satya is said to have cognates in a number of diverse Indo-European languages, including the word "sooth" and "sin" in English, "istina" ("истина") in Russian, "sand" - truthful in Danish/"sann" in Swedish, and "haithya" in Avestan, the liturgical language of Zoroastrianism.
Hinduism.
Vedic literature.
"Satya" is a central theme in the Vedas. It is equated with and considered necessary to the concept Ṛta (Sanskrit ऋतं ṛtaṃ) – that which is properly joined, order, rule, nature, balance, harmony. Ṛta results from Satya in the Vedas, states Holdrege, as it regulates and enables the operation of the universe and everything within it. Satya (truth) is considered essential, and without it, the universe and reality falls apart, cannot function.
In Rigveda, opposed to "rita" and "satya" are "anrita" and "asatya" (falsehood). Truth and truthfulness is considered as a form of reverence for the divine, while falsehood a form of sin. "Satya" includes action and speech that is factual, real, true and reverent to "Ṛta" in Book 1, 4, 6, 7, 9 and 10 of Rigveda. However, "Satya" isn't merely about one's past that is in context in the Vedas, it has one's current and one's future contexts as well. De Nicolás states, that in Rigveda, ""Satya" is the modality of acting in the world of "Sat", as the truth to be built, formed or established".
Upanishads.
"Satya" is a widely discussed concept in various Upanishads, including the Brihadaranyaka Upanishad where "satya" is called the means to Brahman, as well as Brahman (Being, true self). In hymn 1.4.14 of Brihadaranyaka Upanishad, "Satya" (truth) is equated to Dharma (morality, ethics, law of righteousness), as
Taittiriya Upanishad's hymn 11.11 states, "Speak the Satya (truth), conduct yourself according to the Dharma (morality, ethics, law)".
Truth is sought, praised in the hymns of Upanishads, held as one that ultimately, always prevails. The Mundaka Upanishad, for example, states in Book 3, Chapter 1,
Sandilya Upanishad of Atharvanaveda, in Chapter 1, includes ten forbearances as virtues, in its exposition of Yoga. It defines Satya as "the speaking of the truth that conduces to the well being of creatures, through the actions of one's mind, speech or body."
Deussen states that "Satya" is described in the major Upanishads with two layers of meanings - one as empirical truth about reality, another as abstract truth about universal principle, being and the unchanging. Both these ideas are explained in early Upanishads, composed before 500 BC, by variously breaking the word "satya" or "satyam" into two or three syllables. In later Upanishads, the ideas evolve and transcend into "satya" as truth (or truthfulness), and Brahman as the Being, Be-ness, real Self, the eternal.
Epics.
The "Shanti Parva" of the Mahabharata states, "The righteous hold that forgiveness, truth, sincerity and compassion are the foremost (of all virtues). Truth is the essence of the Vedas."
The Epic repeatedly emphasizes that "Satya" is a basic virtue, because everything and everyone depends on and relies on "Satya".
Sutras.
In the Yoga Sutras of Patanjali, it is written, “When one is firmly established in speaking truth, the fruits of action become subservient to him." In Yoga sutra, "Satya" is one of the five yamas, or
virtuous restraints, along with ahimsa (restraint from violence or injury to any living being); asteya (restraint from stealing); brahmacharya (celibacy or restraint from sexually cheating on one's partner); and aparigraha (restraint from covetousness and craving). Patanjali considers "satya" as a restraint from falsehood in one's action (body), words (speech, writing), or feelings / thoughts (mind). In Patanjali's teachings, one may not always know the truth or the whole truth, but one knows if one is creating, sustaining or expressing falsehood, exaggeration, distortion, fabrication or deception. "Satya" is, in Patanjali's Yoga, the virtue of restraint from such falsehood, either through silence or through stating the truth without any form of distortion.
Jainism.
Satya is one of the five vows prescribed in Jain Agamas. Satya was also preached by Mahavira. According to Jainism, not to lie or speak what is not commendable. The underlying cause of falsehood is passion and therefore, it is said to cause "hiṃsā" (injury).
According to the Jain text "Sarvārthasiddhi": "that which causes pain and suffering to the living is not commendable, whether it refers to actual facts or not".
According to Jain text, "Puruşārthasiddhyupāya":
Buddhism.
The term "satya" (Sanskrit; in Pali: "sacca") is translated in English as "reality" or "truth." In terms of the Four Noble Truths ("ariyasacca"), the Pali can be written as "sacca", "tatha", "anannatatha" and "dhamma".
'The Four Noble Truths' ("ariya-sacca") are the briefest synthesis of the entire teaching of Buddhism, since all those manifold doctrines of the threefold Pali canon are, without any exception, included therein. They are the truth of suffering (mundane mental and physical phenomenon), of the origin of suffering (tanha 'pali' the craving), of the extinction of suffering (Nibbana or nirvana), and of the Noble Eightfold Path leading to the extinction of suffering (the eight supra-mundane mind factors ).
Sikhism.
ਜਿਨਾ ਰਾਸਿ ਨ ਸਚੁ ਹੈ ਕਿਉ ਤਿਨਾ ਸੁਖੁ ਹੋਇ ॥ 
Those who do not have the Assets of Truth-how can they find peace? 
ਖੋਟੈ ਵਣਜਿ ਵਣੰਜਿਐ ਮਨੁ ਤਨੁ ਖੋਟਾ ਹੋਇ ॥ 
By dealing their deals of falsehood, their minds and bodies become false. 
ਫਾਹੀ ਫਾਥੇ ਮਿਰਗ ਜਿਉ ਦੂਖੁ ਘਣੋ ਨਿਤ ਰੋਇ ॥੨॥
Like the deer caught in the trap, they suffer in terrible agony; they continually cry out in pain. 
ਖੋਟੇ ਪੋਤੈ ਨਾ ਪਵਹਿ ਤਿਨ ਹਰਿ ਗੁਰ ਦਰਸੁ ਨ ਹੋਇ ॥ 
The counterfeit coins are not put into the Treasury; they do not obtain the Blessed Vision of the Lord-Guru. 
ਖੋਟੇ ਜਾਤਿ ਨ ਪਤਿ ਹੈ ਖੋਟਿ ਨ ਸੀਝਸਿ ਕੋਇ ॥ खोटे जाति न पति है खोटि न सीझसि कोइ ॥
The false ones have no social status or honor. No one succeeds through falsehood. 
ਖੋਟੇ ਖੋਟੁ ਕਮਾਵਣਾ ਆਇ ਗਇਆ ਪਤਿ ਖੋਇ ॥੩॥
Practicing falsehood again and again, people come and go in reincarnation, and forfeit their honor.
ਨਾਨਕ ਮਨੁ ਸਮਝਾਈਐ ਗੁਰ ਕੈ ਸਬਦਿ ਸਾਲਾਹ ॥ 
O Nanak, instruct your mind through the Word of the Guru's Shabad, and praise the Lord. 
ਰਾਮ ਨਾਮ ਰੰਗਿ ਰਤਿਆ ਭਾਰੁ ਨ ਭਰਮੁ ਤਿਨਾਹ ॥ 
Those who are imbued with the love of the Name of the Lord are not loaded down by doubt. 
ਹਰਿ ਜਪਿ ਲਾਹਾ ਅਗਲਾ ਨਿਰਭਉ ਹਰਿ ਮਨ ਮਾਹ ॥੪॥੨੩॥
Those who chant the Name of the Lord earn great profits; the Fearless Lord abides within their minds. ||4||23||
- Guru Granth Sahib (Page 23)
Indian emblem motto.
The motto of the republic of India's emblem is Satyameva Jayate which is literally translated as 'Truth alone triumphs'.