The word(s) "illegal" appears 42 time(s) in 36 verse(s) in Quran in Mohsin Khan translation.

(1) It is made lawful for you to have sexual relations with your wives on the night of As-Saum (the fasts). They are Libas [i.e. body cover, or screen, or Sakan, (i.e. you enjoy the pleasure of living with them - as in Verse 7:189) Tafsir At-Tabari ], for you and you are the same for them. Allah knows that you used to deceive yourselves, so He turned to you (accepted your repentance) and forgave you. So now have sexual relations with them and seek that which Allah has ordained for you (offspring), and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Saum (fast) till the nightfall. And do not have sexual relations with them (your wives) while you are in I'tikaf (i.e. confining oneself in a mosque for prayers and invocations leaving the worldly activities) in the mosques. These are the limits (set) by Allah, so approach them not. Thus does Allah make clear His Ayat (proofs, evidence, lessons, signs, revelations, verses, laws, legal and illegal things, Allah's set limits, orders) to mankind that they may become Al-Muttaqun (the pious - See V.2:2).

(2) And eat up not one another's property unjustly (in any illegal way e.g. stealing, robbing, deceiving, etc.), nor give bribery to the rulers (judges before presenting your cases) that you may knowingly eat up a part of the property of others sinfully.

(3) Shaitan (Satan) threatens you with poverty and orders you to commit Fahsha (evil deeds, illegal sexual intercourse, sins); whereas Allah promises you Forgiveness from Himself and Bounty, and Allah is All-Sufficient for His creatures' needs, All-Knower.

(4) And those who, when they have committed Fahishah (illegal sexual intercourse) or wronged themselves with evil, remember Allah and ask forgiveness for their sins; - and none can forgive sins but Allah - and do not persist in what (wrong) they have done, while they know.

(5) It is not for any Prophet to take illegally a part of booty (Ghulul ), and whosoever deceives his companions as regards the booty, he shall bring forth on the Day of Resurrection that which he took (illegally). Then every person shall be paid in full what he has earned, and they shall not be dealt with unjustly.

(6) Is then one who follows (seeks) the good Pleasure of Allah (by not taking illegally a part of the booty) like the one who draws on himself the Wrath of Allah (by taking a part of the booty illegally - Ghulul)? - his abode is Hell, and worst, indeed is that destination!

(7) And those of your women who commit illegal sexual intercourse, take the evidence of four witnesses from amongst you against them; and if they testify, confine them (i.e. women) to houses until death comes to them or Allah ordains for them some (other) way.

(8) And the two persons (man and woman) among you who commit illegal sexual intercourse, hurt them both. And if they repent (promise Allah that they will never repeat, i.e. commit illegal sexual intercourse and other similar sins) and do righteous good deeds, leave them alone. Surely, Allah is Ever All-Forgiving (the One Who forgives and accepts repentance), (and He is) Most Merciful.

(9) O you who believe! You are forbidden to inherit women against their will; and you should not treat them with harshness, that you may take away part of the Mahr you have given them, unless they commit open illegal sexual intercourse; and live with them honourably. If you dislike them, it may be that you dislike a thing and Allah brings through it a great deal of good.

(10) Also (forbidden are) women already married, except those (slaves) whom your right hands possess. Thus has Allah ordained for you. All others are lawful, provided you seek (them in marriage) with Mahr (bridal-money given by the husband to his wife at the time of marriage) from your property, desiring chastity, not committing illegal sexual intercourse, so with those of whom you have enjoyed sexual relations, give them their Mahr as prescribed; but if after a Mahr is prescribed, you agree mutually (to give more), there is no sin on you. Surely, Allah is Ever All-Knowing, All-Wise.