The word(s) "taint" appears 12 time(s) in 12 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) Who bear in mind the certainty that they are to meet their Lord, and that they are to return to Him.

(2) And remember We took your covenant and We raised above you (the towering height) of Mount (Sinai): (Saying): "Hold firmly to what We have given you, and hearken (to the Law)": They said:" We hear, and we disobey:" And they had to drink into their hearts (of the taint) of the calf because of their Faithlessness. Say: "Vile indeed are the behests of your Faith if ye have any faith!"

(3) If ye are on a journey, and cannot find a scribe, a pledge with possession (may serve the purpose). And if one of you deposits a thing on trust with another, Let the trustee (Faithfully) discharge His trust, and let him fear his Lord. Conceal not evidence; for whoever conceals it,- His heart is tainted with sin. And Allah Knoweth all that ye do.

(4) Allah is He Who raised the heavens without any pillars that ye can see; is firmly established on the throne (of authority); He has subjected the sun and the moon (to his Law)! Each one runs (its course) for a term appointed. He doth regulate all affairs, explaining the signs in detail, that ye may believe with certainty in the meeting with your Lord.

(5) Still less can their knowledge comprehend the Hereafter: Nay, they are in doubt and uncertainty thereanent; nay, they are blind thereunto!

(6) So patiently persevere: for verily the promise of Allah is true: nor let those shake thy firmness, who have (themselves) no certainty of faith.

(7) They shall there exchange, one with another, a (loving) cup free of frivolity, free of all taint of ill.

(8) Not frivolity will they hear therein, nor any taint of ill,-

(9) But verily it is Truth of assured certainty.

(10) And We have set none but angels as Guardians of the Fire; and We have fixed their number only as a trial for Unbelievers,- in order that the People of the Book may arrive at certainty, and the Believers may increase in Faith,- and that no doubts may be left for the People of the Book and the Believers, and that those in whose hearts is a disease and the Unbelievers may say, "What symbol doth Allah intend by this?" Thus doth Allah leave to stray whom He pleaseth, and guide whom He pleaseth: and none can know the forces of thy Lord, except He and this is no other than a warning to mankind.