Hi, Hisalone,
I gave three however if you want me to narrow it down to one I will.
Purgatory.
Show me where it is in the bible?
The honest answer is that it is that there are several sources for this. Chances are, you may not have 2 Maccabees 12:43-46 … that is OK… I’ll give it to you…
“…making a gathering . . . sent twelve thousand drachmas of silver to Jerusalem for sacrifice to be offered for the sins of the dead, thinking well and religiously concerning the resurrection (For if he had not hoped that they that were slain should rise again, it would have seemed superfluous and vain to pray for the dead). And because he considered that they who had fallen asleep with godliness, had great grace laid up for them. It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins”.

But don’t stop there - actually, there are several more …
Here is the link:
newadvent.org/cathen/12575a.htm
And here are some references you can go to in your own Bible:
That temporal punishment is due to sin, even after the sin itself has been pardoned by God, is clearly the teaching of Scripture. God indeed brought man out of his first disobedience and gave him power to govern all things (Wisdom 10:2), but still condemned him “to eat his bread in the sweat of his brow” until he returned unto dust. God forgave the incredulity of Moses and Aaron, but in punishment kept them from the “land of promise” (Numbers 20:12). The Lord took away the sin of David, but the life of the child was forfeited because David had made God’s enemies blaspheme His Holy Name (2 Samuel 12:13-14). In the New Testament as well as in the Old, almsgiving and fasting, and in general penitential acts are the real fruits of repentance (Matthew 3:8; Luke 17:3; 3:3). The whole penitential system of the Church testifies that the voluntary assumption of penitential works has always been part of true repentance and the Council of Trent (Sess. XIV, can. xi) reminds the faithful that God does not always remit the whole punishment due to sin together with the guilt. God requires satisfaction, and will punish sin, and this doctrine involves as its necessary consequence a belief that the sinner failing to do penance in this life may be punished in another world, and so not be cast off eternally from God. (Source: Catholic Encycllpedia)
Ah, and some more…
There are several passages in the New Testament that point to a process of purification after death. Thus, Jesus Christ declares (Matthew 12:32): “And whosoever shall speak a word against the Son of man, it shall be forgiven him: but he that shall speak against the Holy Ghost, it shall not be forgiven him, neither in this world, nor in the world to come.” (Source: Catholic Encycllpedia)
And, then there is St., Paul…(1Cor 3: 11-15) D
“For other foundation no man can lay, but that which is laid; which is Christ Jesus. Now if any man build upon this foundation, gold, silver, precious stones, wood, hay stubble: Every man’s work shall be manifest; for the day of the Lord shall declare it, because it shall be revealed in fire; and the fire shall try every man’s work, of what sort it is. If any man’s work abide, which he hath built thereupon, he shall receive a reward. If any man’s work burn, he shall suffer loss: but he himself shall be saved, yet so as by fire.”
Now, I am not sure how you are disposed to the Early Church Fathers (the group of men who lived from 100AD - 400AD) But, I guess they would not be considered Biblical?
In my opinion there is enough here to make the case that Purgatory is in fact a Biblical concept. I dare say, it is a logical and just concept, too - but, that may be stretching things…
My question to you, Hisalone, and to anyone else who thinks the Bible is ALL THERE IS… how do you explain the meaning of John 21:25 “There are also many other things that Jesus did, but if these were to be described individually, I do not think the whole world would contain the books that would be written.” I am guessing here - but, this does seem to identify that there are real, genuine and significant omissions in the Bible - actual realities that were simply not written down!
I think it would be presumptious to think of them being simply discarded. So, what happened to them? In my opinion, the answer rests in Sacred Tradition. To simply dismiss something because **IT IS NOT IN THE BIBLE **fails to recognize John’s words telling you that there are real things that were not put in the Bible. Since God is the real Author - the assumption is that He knows what He is doing and that these omissions were not accidental but intended.
There was a Chruch BEFORE there was a Bible. “On Pentecost Sunday, the Holy Spirit did not deliver a book.”

The oral teachings of the Apostles, and the teachings of their disciples are what formed Sacred Tradition. And the Holy Spirit was guiding the Church (and, that would be the Catholic Church) in this matter, too.
God Bless