All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
The Mus-haf refers to the papers or sheets on which the Quran is written. All of the variations in the readings that have been confirmed as being Mutawaatir (i.e. being reported by a group of narrators from a group of narrators, generation after generation and so forth, and they are all trustworthy people and it is absolutely impossible for them to agree on a lie) are considered part of the Quran.
This is why we find the Quran reciters transmitting the different modes of recitation with their Mutawaatir chains of transmission from the Prophet, sallallaahu ‘alayhi wa sallam, from Allaah, The Exalted.
The Companions wrote different Mus-hafs (copies of the Quran) using a manner of writing which is suitable for the various modes of recitation. The early Quranic scripts were written without pointing diacritics, Tashkeel (supplementary diacritics; marks used as phonetic guides) or Harakaat (short vowel marks) in order for them to suit the different transmitted modes of recitation.
This has been stated by the author of Al-Muqarrab Al-Mabsoot fi Al-Marsoom wal Madhboot.
As for the extra words that are found in some modes of recitation, they have been written in some Mus-hafs in a manner that suits a certain mode of recitation and in another Quranic script in a different manner suitable for another mode of recitation. For instance, the Arabic verb "وصّى", meaning "instructed" in the verse that reads (what means): {And Ibraaheem (Abraham) instructed his sons ...}[Quran 2:132] is recited as "أوصى" in a different mode of recitation.
In addition, Allaah, The Exalted, says (what means): {And the first forerunners [in the faith] among the Muhajireen and the Ansaar and those who followed them with good conduct - Allaah is pleased with them and they are pleased with Him, and He has prepared for them gardens beneath which (تحتها) rivers flow, wherein they will abide forever. That is the great attainment.}[Quran 9:100] According to the recitation of Al-Makky (Ibn Katheer), the verse reads “… gardens underneath which (من تحتها) rivers flow...”
Another example is the verse that reads (what means): {… then indeed, Allaah is (هو) the Free of need, the Praiseworthy.}[Quran 57:24] The verse is written in the Madani and Shaami Mus-hafs (Naaf'i, Ibn 'Aamir and Abu J'afar) without the pronoun “هو”, meaning “He," in English.
Another example is the letter “و" meaning “and,” in the verse that reads (what means): {And hasten (وسارعوا)…}[Quran 3:133] as, according to other modes of recitation (the Madani and Shaami Mus-hafs), the verse does not begin with it.
It should be noted that what is written in the Lawh Al-Mahfooth (Preserved Tablet) is considered part of the Unseen; we only know about its details through divine revelation. We have not found any details about this matter in the revelation (the Quran and the Sunnah) or the opinions of the Muslim scholars. Therefore, no one should enter into false discourse about it without having knowledge.