صدق
Ṣidq
Truthfulness and sincerity; the verbal noun of sadaqa, to speak the truth and keep one’s word.
What it means
Ṣidq is the verbal noun of ṣadaqa, to speak truly. It means truthfulness in speech, and also sincerity of intention and faithfulness in action, so that a person’s word, belief and conduct agree. The Quran says, “O you who believe, fear God and be with the truthful” (9:119). The word appears in praise of the prophets. Abraham asks for “a tongue of truth among the later generations” (26:84), and Ismail and Idris are called truthful (19:54, 19:56). A person marked by great truthfulness is a ṣiddīq, the title given to Abu Bakr. The related word ṣadaqa, charity, comes from the same root, because giving shows that a person’s faith is true.
Often misunderstood as
Rendering sidq only as “honesty” covers speech alone, while the Arabic also includes sincerity of heart and fidelity in deeds.
What the sources say
The Prophet Muhammad (peace be upon him) said that truthfulness leads to righteousness and righteousness leads to Paradise, and that lying leads to wrongdoing and wrongdoing to the Fire (Sahih al-Bukhari and Sahih Muslim). Before his mission the Meccans called him al-Amin, the trustworthy.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 35, listed as ṢIDQ. The definition is restated here.