The word(s) "doubt" appears 83 time(s) in 78 verse(s) in Quran in Abdullah Yusuf Ali translation.

(31) Has not the story reached you, (O people!), of those who (went) before you? - of the people of Noah, and 'Ad, and Thamud? - And of those who (came) after them? None knows them but Allah. To them came messengers with Clear (Signs); but they put their hands up to their mouths, and said: "We do deny (the mission) on which ye have been sent, and we are really in suspicious (disquieting) doubt as to that to which ye invite us."

(32) Their messengers said: "Is there a doubt about Allah, The Creator of the heavens and the earth? It is He Who invites you, in order that He may forgive you your sins and give you respite for a term appointed!" They said: "Ah! ye are no more than human, like ourselves! Ye wish to turn us away from the (gods) our fathers used to worship: then bring us some clear authority."

(33) We have, without doubt, sent down the Message; and We will assuredly guard it (from corruption).

(34) They said: "Yea, we have come to thee to accomplish that of which they doubt.

(35) Undoubtedly Allah doth know what they conceal, and what they reveal: verily He loveth not the arrogant.

(36) They attribute to Allah what they hate (for themselves), and their tongues assert the falsehood that all good things are for themselves: without doubt for them is the Fire, and they will be the first to be hastened on into it!

(37) Without doubt, in the Hereafter they will perish.

(38) See they not that Allah, Who created the heavens and the earth, has power to create the like of them (anew)? Only He has decreed a term appointed, of which there is no doubt. But the unjust refuse (to receive it) except with ingratitude.

(39) Thus did We make their case known to the people, that they might know that the promise of Allah is true, and that there can be no doubt about the Hour of Judgment. Behold, they dispute among themselves as to their affair. (Some) said, "Construct a building over them": Their Lord knows best about them: those who prevailed over their affair said, "Let us surely build a place of worship over them."

(40) (Some) say they were three, the dog being the fourth among them; (others) say they were five, the dog being the sixth,- doubtfully guessing at the unknown; (yet others) say they were seven, the dog being the eighth. Say thou: "My Lord knoweth best their number; It is but few that know their (real case)." Enter not, therefore, into controversies concerning them, except on a matter that is clear, nor consult any of them about (the affair of) the Sleepers.