The word(s) "once" appears 119 time(s) in 116 verse(s) in Quran in Abdullah Yusuf Ali translation.

(41) If they could find a place to flee to, or caves, or a place of concealment, they would turn straightaway thereto, with an obstinate rush.

(42) They will present their excuses to you when ye return to them. Say thou: "Present no excuses: we shall not believe you: Allah hath already informed us of the true state of matters concerning you: It is your actions that Allah and His Messenger will observe: in the end will ye be brought back to Him Who knoweth what is hidden and what is open: then will He show you the truth of all that ye did."

(43) See they not that they are tried every year once or twice? Yet they turn not in repentance, and they take no heed.

(44) If Allah were to hasten for men the ill (they have earned) as they would fain hasten on the good,- then would their respite be settled at once. But We leave those who rest not their hope on their meeting with Us, in their trespasses, wandering in distraction to and fro.

(45) Behold! they fold up their hearts, that they may lie hid from Him! Ah even when they cover themselves with their garments, He knoweth what they conceal, and what they reveal: for He knoweth well the (inmost secrets) of the hearts.

(46) But when he saw their hands went not towards the (meal), he felt some mistrust of them, and conceived a fear of them. They said: "Fear not: We have been sent against the people of Lut."

(47) We certainly gave the Book to Moses, but differences arose therein: had it not been that a word had gone forth before from thy Lord, the matter would have been decided between them, but they are in suspicious doubt concerning it.

(48) Then there came a caravan of travellers: they sent their water-carrier (for water), and he let down his bucket (into the well)... He said: "Ah there! Good news! Here is a (fine) young man!" So they concealed him as a treasure! But Allah knoweth well all that they do!

(49) Such is one of the stories of what happened unseen, which We reveal by inspiration unto thee; nor wast thou (present) with them then when they concerted their plans together in the process of weaving their plots.

(50) It is the same (to Him) whether any of you conceal his speech or declare it openly; whether he lie hid by night or walk forth freely by day.