The word(s) "doubt" appears 83 time(s) in 77 verse(s) in Quran in Mohsin Khan translation.

(71) "Hinderer of good, transgressor, doubter,

(72) Then which of the Graces of your Lord (O man!) will you doubt?

(73) And he [Lut (Lot)] indeed had warned them of Our Seizure (punishment), but they did doubt the warnings!

(74) (The hypocrites) will call the believers: "Were we not with you?" The believers will reply: "Yes! But you led yourselves into temptations, you looked forward for our destruction; you doubted (in Faith) and you were deceived by false desires, till the Command of Allah came to pass. And the chief deceiver (Satan) deceived you in respect of Allah."

(75) And those of your women as have passed the age of monthly courses, for them the 'Iddah (prescribed period), if you have doubt (about their periods), is three months; and for those who have no courses [(i.e. they are still immature) their 'Iddah (prescribed period) is three months likewise, except in case of death] . And for those who are pregnant (whether they are divorced or their husbands are dead), their 'Iddah (prescribed period) is until they lay down their burden; and whosoever fears Allah and keeps his duty to Him, He will make his matter easy for him.

(76) And We have set none but angels as guardians of the Fire. And We have fixed their number (19) only as a trial for the disbelievers, in order that the people of the Scripture (Jews and Christians) may arrive at a certainty [that this Qur'an is the truth as it agrees with their Books regarding the number (19) which is written in the Taurat (Torah) and the Injeel (Gospel)] and that the believers may increase in Faith (as this Qur'an is the truth), and that no doubt may be left for the people of the Scripture and the believers, and that those in whose hearts is a disease (of hypocrisy) and the disbelievers may say: "What Allah intends by this (curious) example ?" Thus Allah leads astray whom He wills and guides whom He wills. And none can know the hosts of your Lord but He. And this (Hell) is nothing else than a (warning) reminder to mankind.

(77) That is (without doubt) the True Day. So, whosoever wills, let him seek a place with (or a way to) His Lord (by obeying Him in this worldly life)!