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

(11) Among the people of the Scripture (Jews and Christians) is he who, if entrusted with a Qintar (a great amount of wealth, etc.), will readily pay it back; and among them there is he who, if entrusted with a single silver coin, will not repay it unless you constantly stand demanding, because they say: "There is no blame on us to betray and take the properties of the illiterates (Arabs)." But they tell a lie against Allah while they know it.

(12) And to Allah belongs all that is in the heavens and all that is in the earth. And all matters go back (for decision) to Allah.

(13) They will do you no harm, barring a trifling annoyance; and if they fight against you, they will show you their backs, and they will not be helped.

(14) Muhammad (صلى الله عليه وسلم) is no more than a Messenger, and indeed (many) Messengers have passed away before him. If he dies or is killed, will you then turn back on your heels (as disbelievers)? And he who turns back on his heels, not the least harm will he do to Allah; and Allah will give reward to those who are grateful.

(15) O you who believe! If you obey those who disbelieve, they will send you back on your heels, and you will turn back (from Faith) as losers.

(16) (And remember) when you ran away (dreadfully) without even casting a side glance at anyone, and the Messenger (Muhammad صلى الله عليه وسلم) was in your rear calling you back. There did Allah give you one distress after another by way of requital to teach you not to grieve for that which had escaped you, nor for that which had befallen you. And Allah is Well-Aware of all that you do.

(17) Those of you who turned back on the day the two hosts met (i.e. the battle of Uhud), it was Shaitan (Satan) who caused them to backslide (run away from the battlefield) because of some (sins) they had earned. But Allah, indeed, has forgiven them. Surely, Allah is Oft-Forgiving, Most Forbearing.

(18) (And remember) when Allah took a covenant from those who were given the Scripture (Jews and Christians) to make it (the news of the coming of Prophet Muhammad صلى الله عليه وسلم and the religious knowledge) known and clear to mankind, and not to hide it, but they threw it away behind their backs, and purchased with it some miserable gain! And indeed worst is that which they bought.

(19) But if you intend to replace a wife by another and you have given one of them a Qintar (of gold i.e. a great amount as Mahr) take not the least bit of it back; would you take it wrongfully without a right and (with) a manifest sin?

(20) And how could you take it (back) while you have gone in unto each other, and they have taken from you a firm and strong covenant?