I understand that there cannot be any revelations outside the Bible--all revelations are over.  But how can we say that gifts are not in operation now?  Is there any clear text stating that there will not be gifts in days to come?  "In the last days, I will pour out my Spirit on all flesh: and they shall prophesy."--Isn't this promise still applicable?

Answer

1.  The "Last days" it refers to is the present era of redemptive history from the first coming of Christ to His return. (Heb. 1:2; 1 Pet. 1:20; 1 John 2:18).  So, we have seen that when Christ came that He did pour out His Spirit and there was prophecy.

2.  Now the question...are we to expect the same display of the Spirit's power and actions from the first coming to the second coming?  Not really.  You see, although "Jesus is the same yesterday, today, and forever," His interaction with mankind changes as to the purpose that He has for men and women.

When Jesus came the first time He had to establish His credentials as the Messiah, which was to fulfill prophecy about the Messiah and also to demonstrate His power over creation, the angelic forces, and the spiritual world.  Thus we see Jesus walking on water, commanding the wind to stop blowing, raising the dead, etc.  Jesus also gave some miraculous powers to the Apostles and those disciples closely associated to those Apostles.....again the purpose was to validate Christ's Messiahship and the authority of those disciples to speak for God and Christ.  We see this validation with miracles and the sign gifts.  But after Christ was rejected and crucified and raised to life, and after the Scriptures were being recorded we see that the "sign gifts" and the miraculous powers died out--their purpose was over.

Today, we validate our message, as being from God, by simply comparing it to the Bible--God's Word.  We don't need miracles or sign gifts to validate what we say is true.  We are calling people to believe by faith and not by sight, and to verify our message by the Word of God.

3.  One evidence that the "sign gifts" have ceased is the quality of the the gifts claimed to exist today:

"Gift of Tongues" - the original and "only" valid operation of that gift was the ability to speak in a "known language" that was not learned by the speaker previously.  It is what we see at Pentecost, where simple Galileans could speak in foreign languages they never studied.  This was the ONLY valid action of this gift.  To claim that today's "speaking in gibberish" or "having a private prayer language" is evidence that it is not the same gift--thus invalid.  If the Charismatics/Pentecostals truly had the true "gift of tongues" then they would not have to send their missionaries to language school prior to going to the mission field.

"Healings" -- Look at the original gift of healings in the time of Christ and the Apostles--the healings were organic, that is, they were miraculous healings causing flesh to be replaced, or deformities to be corrected--INSTANTLY!  There was no rehabilitation process...the person crippled for 40 years could not only stand up, but could walk and jump instantly without any training whatsoever!  Jesus could take a person who was in the grave four days, whose flesh was decayed to the point that their face would not be recognizable, and create new flesh and bring the person back from the dead.

What we see today is bogus, such as claiming the gift of healings when backaches are cured, post-nasal drip is cured...this is not the gift of healings, but a counterfeit.  Along with all the other counterfeit gifts of the Spirit claimed today: Slaying in the Spirit, Holy Laughter, and Vomiting in the Spirit--what a mockery of God the Father, God the Son, and God the Holy Spirit.

You ask for the verse that says the gifts will cease, well, show me the verse that says there is a Trinity--you won't find any.  Yet we don't deny the existence of the Trinity, because various verses put together give clear evidence of the existence of a Trinity.  Likewise, when we make a proper study of Scripture we see that the "sign gifts" and "miracles" only occurred in three basic periods over the History of God's people:

1. The time of Moses, 2. The time of Elijah and Elisha, and the time of Christ and the Apostles.  They were always, always, associated with the giving of new revelation by God.  As you said earlier, the Canon is closed, there is no more revelation, thus no more need for signs and wonders.