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

(31) Except for those who (having fled away and then) came back (as Muslims) with repentance before they fall into your power; in that case, know that Allah is Oft-Forgiving, Most Merciful.

(32) O you who believe! Whoever from among you turns back from his religion (Islam), Allah will bring a people whom He will love and they will love Him; humble towards the believers, stern towards the disbelievers, fighting in the Way of Allah, and never fear of the blame of the blamers. That is the Grace of Allah which He bestows on whom He wills. And Allah is All-Sufficient for His creatures' needs, All-Knower.

(33) Lawful to you is (the pursuit of) water-game and its use for food - for the benefit of yourselves and those who travel, but forbidden is (the pursuit of) land-game as long as you are in a state of Ihram (for Hajj or 'Umrah). And fear Allah to Whom you shall be gathered back.

(34) If you could but see when they will be held over the (Hell) Fire! They will say: "Would that we were but sent back (to the world)! Then we would not deny the Ayat (proofs, evidence, verses, lessons, revelations, etc.) of our Lord, and we would be of the believers!"

(35) They indeed are losers who denied their Meeting with Allah, until all of a sudden, the Hour (signs of death) is on them, and they say: "Alas for us that we gave no thought to it," while they will bear their burdens on their backs; and evil indeed are the burdens that they will bear!

(36) Say (O Muhammad صلى الله عليه وسلم): "Shall we invoke others besides Allah (false deities), that can do us neither good nor harm, and shall we turn back on our heels after Allah has guided us (to true Monotheism)? - like one whom the Shayatin (devils) have made to go astray in the land in confusion, his companions calling him to guidance (saying): 'Come to us.' " Say: "Verily, Allah's Guidance is the only guidance, and we have been commanded to submit (ourselves) to the Lord of the 'Alamin (mankind, jinn and all that exists);

(37) And unto those who are Jews, We forbade every (animal) with undivided hoof, and We forbade them the fat of the ox and the sheep except what adheres to their backs or their entrails, or is mixed up with a bone. Thus We recompensed them for their rebellion [committing crimes like murdering the Prophets and eating of Riba (usury)]. And verily, We are Truthful.

(38) If they (Jews) belie you (Muhammad صلى الله عليه وسلم) say: "Your Lord is the Owner of Vast Mercy, and never will His Wrath be turned back from the people who are Mujrimun (criminals, polytheists or sinners)."

(39) Await they just for the final fullfilment of the event? On the Day the event is finally fulfilled (i.e. the Day of Resurrection), those who neglected it before will say: "Verily, the Messengers of our Lord did come with the truth, now are there any intercessors for us that they might intercede on our behalf? Or could we be sent back (to the first life of the world) so that we might do (good) deeds other than those (evil) deeds which we used to do?" Verily, they have lost their ownselves (i.e. destroyed themselves) and that which they used to fabricate (invoking and worshipping others besides Allah) has gone away from them.

(40) O you who believe! When you meet those who disbelieve, in a battle-field, never turn your backs to them.