The word(s) "four" appears 21 time(s) in 18 verse(s) in Quran in Mohsin Khan translation.

(11) And those who accuse chaste women, and produce not four witnesses, flog them with eighty stripes, and reject their testimony forever. They indeed are the Fasiqun (liars, rebellious, disobedient to Allah).

(12) And for those who accuse their wives, but have no witnesses except themselves, let the testimony of one of them be four testimonies (i.e. testifies four times) by Allah that he is one of those who speak the truth.

(13) But it shall avert the punishment (of stoning to death) from her, if she bears witness four times by Allah, that he (her husband) is telling a lie.

(14) Why did they not produce four witnesses? Since they (the slanderers) have not produced witnesses! Then with Allah they are the liars.

(15) Allah has created every moving (living) creature from water. Of them there are some that creep on their bellies, and some that walk on two legs, and some that walk on four. Allah creates what He wills. Verily Allah is Able to do all things.

(16) All the praises and thanks be to Allah, the (only) Originator [or the (Only) Creator] of the heavens and the earth, Who made the angels messengers with wings, two or three or four. He increases in creation what He wills. Verily, Allah is Able to do all things.

(17) He placed therein (i.e. the earth) firm mountains from above it, and He blessed it, and measured therein its sustenance (for its dwellers) in four Days equal (i.e. all these four days were equal in the length of time) for all those who ask (about its creation).

(18) Have you not seen that Allah knows whatsoever is in the heavens and whatsoever is on the earth? There is no Najwa (secret counsel) of three but He is their fourth (with His Knowledge, while He Himself is over the Throne, over the seventh heaven), nor of five but He is their sixth (with His Knowledge), nor of less than that or more but He is with them (with His Knowledge) wheresoever they may be. And afterwards on the Day of Resurrection He will inform them of what they did. Verily, Allah is the All-Knower of everything.