Volume 8, Book 82, Number 817: Sahih Bukhari
Narrated Ibn Abbas:
*In the meantime, 'Umar sat on the pulpit and when the callmakers for the prayer had finished their call, 'Umar stood up, and having glorified and praised Allah as He deserved, he said, "Now then, I am going to tell you something which (Allah) has written for me to say. I do not know; perhaps it portends my death, so whoever understands and remembers it, must narrate it to the others wherever his mount takes him, but if somebody is afraid that he does not understand it, then it is unlawful for him to tell lies about me. Allah sent Muhammad with the Truth and revealed the Holy Book to him, and among what Allah revealed, was the Verse of the Rajam (the stoning of married person (male & female) who commits illegal sexual intercourse, and we did recite this Verse and understood and memorized it. Allah’s Apostle did carry out the punishment of stoning and so did we after him. *
*I am afraid that after a long time has passed, somebody will say, ‘By Allah, we do not find the Verse of the Rajam in Allah’s Book,’ and thus they will go astray by leaving an obligation which Allah has revealed. And the punishment of the Rajam is to be inflicted to any married person (male & female), who commits illegal sexual intercourse, if the required evidence is available or there is conception or confession. **And then we used to recite among the Verses in Allah’s Book: ‘O people! Do not claim to be the offspring of other than your fathers, as it is disbelief (unthankfulness) on your part that you claim to be the offspring of other than your real father.’ **Then Allah’s Apostle said, ‘Do not praise me excessively as Jesus, son of Marry was praised, but call me Allah’s Slave and His Apostles.’ (O people!) I have been informed that a speaker amongst you says, 'By Allah, if ‘Umar should die, I will give the pledge of allegiance to such-and-such person.’ One should not deceive oneself by saying that the pledge of allegiance given to Abu Bakr was given suddenly and it was successful. No doubt, it was like that, but Allah saved (the people) from its evil, and there is none among you who has the qualities of Abu Bakr. Remember that whoever gives the pledge of allegiance to anybody among you without consulting the other Muslims, neither that person, nor the person to whom the pledge of allegiance was given, are to be supported, lest they both should be killed. *
So it seems your own hadith talk about verses missing. Ibn Hanbal recorded a hadith by Aisha regarding this missing verse about stoning adulterers:
Aisha reported:
“When the verses “Rajm” [Stoning] and ayah “Rezah Kabir” descended, they were written on a piece of paper and kept under my pillow. Following the demise of Prophet Muhammad (S) a goat ate the piece of paper while we were mourning.”
Another translation says:
“The verse of stoning and of suckling an adult ten times were revealed, and they were (written) on a paper and kept under my bed. When the Messenger of Allah (SAWW.) expired and we were preoccupied with his death, a goat entered and ate away the paper.”
Al-Muttaqi ‘Ali bin Husam al-Din](http://pressthat.wordpress.com/w/index.php?title=Al-Muttaqi_'Ali_bin_Husam_al-Din&action=edit)* in his book “Mukhtasar Kanz al-’Ummal](http://pressthat.wordpress.com/w/index.php?title=Mukhtasar_Kanz_al-'Ummal&action=edit)” printed on the margin of *Musnad Ahmad ibn Hanbal](Musnad Ahmad ibn Hanbal - Wikipedia), Volume 2, page 2, in his hadith about chapter 33
So it seems Sunnis believe the Quran we have today is missng. I even read a fatwa by a Sunni cleric proudly confirm this. And you are asking me how do I know the Quran is complete!
The Quran is a sign of God among many signs of God. Many early followers of the prophet believed in him before the Quran was completed. In fact some even believed in him very early when the Quran was just being revealed and many died that way without even hearing most of the Quran. Moses’s stick turning to snake is a sign and so is Jesus raising the dead. The magicians of the Pharoah bowed down and proclaimed the God of Moses when they say Moses turning the rod to a snake. The Quran says there are many of God’s signs:
Quran 30 : 20 -26
Among His signs is [the fact] that he has created you from dust; then you were propagated as human beings.
Among His signs is that He has created spouses for you from among yourselves so that you may console yourselves with them. He has planted affection and mercy between you; in that are signs for people who think things over.
Among His signs are the creation of Heaven and Earth, as well as the diversity in your tongues and colors. In that are signs for those who know.
Among His signs are your sleeping at night and by day, and your pursuit of His bounty. In that are signs for any folk who listen.
Among His signs is how He shows you lightning for both fear and anticipation. He sends water down from the sky so He may revive the earth with it following its death. In that are signs for folk who use their reason.
Among His signs are [the fact] that the sky and earth hold firm at His command. Then whenever He calls you forth out of the earth once and for all, you will (all) come forth! * Anyone who is in Heaven and Earth belongs to Him; all are subservient to Him.
Quran 41:37
and among his signs are the night and the day and the sun and the moon; do not prostrate to the sun nor to the moon; and prostrate to Allah who created them, if Him it is that you serve.
So the Quran is a sign among many of God’s signs.