The word(s) "regret" appears 19 time(s) in 19 verse(s) in Quran in Saheeh International translation.

(1) Those who followed will say, "If only we had another turn [at worldly life] so we could disassociate ourselves from them as they have disassociated themselves from us." Thus will Allah show them their deeds as regrets upon them. And they are never to emerge from the Fire.

(2) O you who have believed, do not be like those who disbelieved and said about their brothers when they traveled through the land or went out to fight, "If they had been with us, they would not have died or have been killed," so Allah makes that [misconception] a regret within their hearts. And it is Allah who gives life and causes death, and Allah is Seeing of what you do.

(3) Then Allah sent a crow searching in the ground to show him how to hide the disgrace of his brother. He said, "O woe to me! Have I failed to be like this crow and hide the body of my brother?" And he became of the regretful.

(4) So you see those in whose hearts is disease hastening into [association with] them, saying, "We are afraid a misfortune may strike us." But perhaps Allah will bring conquest or a decision from Him, and they will become, over what they have been concealing within themselves, regretful.

(5) Those will have lost who deny the meeting with Allah, until when the Hour [of resurrection] comes upon them unexpectedly, they will say, "Oh, [how great is] our regret over what we neglected concerning it," while they bear their burdens on their backs. Unquestionably, evil is that which they bear.

(6) And when regret overcame them and they saw that they had gone astray, they said, "If our Lord does not have mercy upon us and forgive us, we will surely be among the losers."

(7) Indeed, those who disbelieve spend their wealth to avert [people] from the way of Allah. So they will spend it; then it will be for them a [source of] regret; then they will be overcome. And those who have disbelieved - unto Hell they will be gathered.

(8) And [He also forgave] the three who were left behind [and regretted their error] to the point that the earth closed in on them in spite of its vastness and their souls confined them and they were certain that there is no refuge from Allah except in Him. Then He turned to them so they could repent. Indeed, Allah is the Accepting of repentance, the Merciful.

(9) And if each soul that wronged had everything on earth, it would offer it in ransom. And they will confide regret when they see the punishment; and they will be judged in justice, and they will not be wronged

(10) And warn them, [O Muhammad], of the Day of regret, when the matter will be concluded; and [yet], they are in [a state of] heedlessness, and they do not believe.