Where?
2 Peter 3:3-4New King James Version (NKJV)
3 knowing this first: that scoffers will come in the last days, walking according to their own lusts, 4 and saying, Where is the promise of His coming? For since the fathers fell asleep, all things continue as they were from the beginning of creation.
Now this verse refers more to the second coming.
With regard to the “rapture” (I think the Greek word actually used means more like “snatching away”), this verse is the one pointed to:
1 Thessalonians 4:16-17New King James Version (NKJV)
16 For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. 17 Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord.
There is lots of disagreement with regard to the timing of this event.
With regard to your question, hope this helps!
2 Peter 3:3-4a