"No falsehood can approach it from before or behind it: It is sent down by One Full of Wisdom, Worthy of all Praise." Al-Quran 41:42
It is alledged that Imam Khomeni (RA) said in his book, Kashf al-Asrar that it was easy for Sahaba to add verses to Quran.
Did Sahaba really tried to add/remove verses from the Glorious Quran. Let's see Imam Khomaini's (RA) statement in the light of Hadith from Sahih Muslim.
Hadith from Sahih Muslim:
Abu Harb b. Abu al-Aswad reported on the authority of his father that Abu Musa al-Ash'ari sent for the reciters of Basra. They came to him and they were three hundred in number. They recited the Qur'an and he said: You are the best among the inhabitants of Basra, for you are the reciters among them. So continue to recite it. (But bear in mind) that your reciting for a long time may not harden your hearts as were hardened the hearts of those before you. We used to recite a surah which resembled in length and severity to (Surah) Bara'at. I have, however, forgotten it with the exception of this which I remember out of it:" If there were two valleys full of riches, for the son of adam, he would long for a third valley, and nothing would fill the stomach of the son of adam but dust." And we used so recite a slirah which resembled one of the surahs of Musabbihat, and I have forgotten it, but remember (this much) out of it:" Oh people who believe, why do you say that which you do not practise" (lxi 2.) and" that is recorded in your necks as a witness (against you) and you would be asked about it on the Day of Resurrection" (xvii. 13).
Sahih Muslim Book 5, Number 2286
The Book of Zakat (Kitab Al-Zakat)
According to Sahih Muslim Abu Musa al-Ash'ari recited 3 verses in front of three hundred people (all reciters of Quran). The last two verses are from Quran.
However, the first one, "If there were two valleys full of riches, for the son of adam, he would long for a third valley, and nothing would fill the stomach of the son of adam but dust.") was an attempt of TEHREEF because this verse is not existing anywhere in the Holy Quran.
Also this Full sura the size of Surah Bara'at he is talking about does not exist.
Similar attempts were made in India to add verses to the Holy Quran by some individuals. These futile attempts were in the form of Sura-e-Wilaya and Sura-e-Nurain. Shias deny these and hold those who attempted as grave sinners. God send only one Quran to the mankind and Shia Muslims share the same with other Muslims.
Thus, Allah SWT has taken the responsibility of the protection of Quran and no individual can add/modify or remove the verses from the Holy Quran.
Shias strictly believe that the present Quran is complete as revealed and it is protected from corruption by Allah SWT. Whoever doesn't belief this is denying the Quranic verses of the God. But it is constantly alledged that Shias believe the in-completeness of the Holy Quran and this belief is a part of their Taqiyya.
The topic of Tahreef is discussed by Shias & Sunnis and solved by both. Here's a wonderful article. Read & judge it yourselves.
Tahreef al-QURAN More information here...please click here...