This is true. The rapture of the living believers and the resurrection of those believers who have died in the Lord can take place at any time. All we are told is that it is the next event for the believer in Christ. The believer’s eternal destiny is to “be with the Lord forever,” either when we pass on or when the rapture takes place, whichever one comes first. If the rapture takes place first, those who are alive during that time will be glorified without experiencing death.
The Scripture where this is found is in I Corinthians 15:20-23: “But Christ has indeed been raised from the dead, the first-fruits of those who have fallen asleep. For since death came through a man, the resurrection of the dead comes through a man. For as in Adam all die, so in Christ all will be made alive. But each in his own turn: Christ, the first-fruits; then when he comes, those who belong to Him”.
Here the Scripture tells us the order of the resurrection: “But each in his own turn: Christ, the first-fruits; then when He comes, those who belong to Him”.
We are told that Christ is the first-fruits of the resurrection, after this would come those who belong to Him, meaning all believers. In verse 23 we are told that Christ, the first-fruits has already been raised! This would be followed by those “who belong to Him”.
Since the order of the resurrection has already begun and Christ the firstfruits has already been raised from the dead, the next event on the agenda in the order of the resurrection, is “when He comes, those who belong to Him”. This will take place before the tribulation begins.