Truthfulness (Sidq) in the Quran in the Holy Quran

(177) Righteousness is not that you turn your faces toward the east or the west, but [true] righteousness is [in] one who believes in Allah, the Last Day, the angels, the Book, and the prophets and gives wealth, in spite of love for it, to relatives, orphans, the needy, the traveler, those who ask [for help], and for freeing slaves; [and who] establishes prayer and gives zakah; [those who] fulfill their promise when they promise; and [those who] are patient in poverty and hardship and during battle. Those are the ones who have been true, and it is those who are the righteous.

(17) The patient, the true, the obedient, those who spend [in the way of Allah], and those who seek forgiveness before dawn.

(119) Allah will say, "This is the Day when the truthful will benefit from their truthfulness." For them are gardens [in Paradise] beneath which rivers flow, wherein they will abide forever, Allah being pleased with them, and they with Him. That is the great attainment.

(119) O you who have believed, fear Allah and be with those who are true.

(8) That He may question the truthful about their truth. And He has prepared for the disbelievers a painful punishment.

(23) Among the believers are men true to what they promised Allah. Among them is he who has fulfilled his vow [to the death], and among them is he who awaits [his chance]. And they did not alter [the terms of their commitment] by any alteration -

(24) That Allah may reward the truthful for their truth and punish the hypocrites if He wills or accept their repentance. Indeed, Allah is ever Forgiving and Merciful.

(35) Indeed, the Muslim men and Muslim women, the believing men and believing women, the obedient men and obedient women, the truthful men and truthful women, the patient men and patient women, the humble men and humble women, the charitable men and charitable women, the fasting men and fasting women, the men who guard their private parts and the women who do so, and the men who remember Allah often and the women who do so - for them Allah has prepared forgiveness and a great reward.

(33) And the one who has brought the truth and [they who] believed in it - those are the righteous.

(34) They will have whatever they desire with their Lord. That is the reward of the doers of good -

(35) That Allah may remove from them the worst of what they did and reward them their due for the best of what they used to do.

(21) Obedience and good words. And when the matter [of fighting] was determined, if they had been true to Allah, it would have been better for them.

(15) The believers are only the ones who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. It is those who are the truthful.