Where in the scriptures does it say that one can still be saved after the rapture and during the tribulation period?
Evidence that many will be saved after the rapture can be found in three places. When John saw a great multitude arriving in Heaven all dressed in white, an angel told him, These are they who have out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.” (Rev. 7:14)
The word translated “out of” means out of the time and place of the Great Tribulation, meaning they will be martyred in the first half of Daniel’s 70th week.
There is evidence that many more will be saved during the Great Tribulation (The second half of Daniel’s 70th week) as well. In Rev. 14:13 we read,
Then I heard a voice from heaven say, “Write: Blessed are the dead who die in the Lord from now on”.
“Yes,” says the Spirit, “they will rest from their labor, for their deeds will follow them.”
Finally, in Rev. 20:4 we’re told that Tribulation believers who will be martyred for their faith will be raised from the dead at the time of the 2nd Coming.