The word(s) "back" appears 161 time(s) in 150 verse(s) in Quran in Mohsin Khan translation.

(131) Bring back the soul (to its body), if you are truthful?

(132) On the Day when the hypocrites - men and women - will say to the believers: "Wait for us! Let us get something from your light!" It will be said: "Go back to your rear! Then seek a light!" So a wall will be put up between them, with a gate therein. Inside it will be mercy, and outside it will be torment."

(133) Those among you who make their wives unlawful to them by (Zihar الظهار) (i.e. by saying to them "You are like my mother's back,") they cannot be their mothers. None can be their mothers except those who gave them birth. And verily, they utter an ill word and a lie. And verily, Allah is Oft-Pardoning, Oft-Forgiving.

(134) Surely, if they (the Jews) are expelled, never will they (hypocrites) go out with them; and if they are attacked, they will never help them. And (even) if they do help them, they (hypocrites) will turn their backs, and they will not be victorious.

(135) O you who believe! When believing women come to you as emigrants, examine them; Allah knows best as to their Faith, then if you ascertain that they are true believers send them not back to the disbelievers. They are not lawful (wives) for the disbelievers nor are the disbelievers lawful (husbands) for them. But give them (the disbelievers) that (amount of money) which they have spent [as their Mahr] to them. And there will be no sin on you to marry them if you have paid their Mahr to them. Likewise hold not the disbelieving women as wives, and ask for (the return of) that which you have spent (as Mahr ) and let them (the disbelievers) ask back for that which they have spent. That is the Judgement of Allah, He judges between you. And Allah is All-Knowing, All-Wise.

(136) And if any of your wives have gone from you to the disbelievers, (as apostates and you asked them to return back your Mahr but they refused) - then you went out for a Ghazwah (military expedition) (against them and) gained booty; then pay from that booty to those whose wives have gone, the equivalent of what they had spent (on their Mahr ). And fear Allah in Whom you believe.

(137) Say (to them): "Verily, the death from which you flee will surely meet you, then you will be sent back to (Allah), the All-Knower of the unseen and the seen, and He will tell you what you used to do."

(138) O Prophet (صلى الله عليه وسلم)! When you divorce women, divorce them at their 'Iddah (prescribed periods) and count (accurately) their 'Iddah (periods ). And fear Allah your Lord (O Muslims). And turn them not out of their (husband's) homes nor shall they (themselves) leave, except in case they are guilty of some open illegal sexual intercourse. And those are the set limits of Allah. And whosoever transgresses the set limits of Allah, then indeed he has wronged himself. You (the one who divorces his wife) know not it may be that Allah will afterward bring some new thing to pass (i.e. to return her back to you if that was the first or second divorce).

(139) Then when they are about to attain their term appointed, either take them back in a good manner or part with them in a good manner. And take as witness two just persons from among you (Muslims). And establish the testimony for Allah. That will be an admonition given to him who believes in Allah and the Last Day. And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).

(140) Calling (all) such as turn their backs and turn away their faces (from Faith) [picking and swallowing them up from that great gathering of mankind on the Day of Resurrection just as a bird picks up a food-grain from the earth with its beak and swallows it up] (Tafsir Al-Qurtubi)