davidmacd.com/catholic/purgatory.htm#Praying%20for%20Souls
The word “Purgatory” is not in the Bible. This has fed a lot of arguments against it. But let us look at another word that is not in the Bible - “Trinity.” For that matter, the word “Bible” itself does not appear in Scripture.
Some Evangelicals say “
everything that is true is in the Bible.” Catholics say that
"everything that is in the Bible is true." There is a subtle distinction. Many Evangelicals would say “if its true its in the Bible, if its not true its not in the Bible.” But the early Christians didn’t have a Bible. It wasn’t written for at least a hundred years and the exact books to include were not formally decided upon until the 300’s. So the tradition of the Church is important. Catholics believe there are spiritual truths that are inferred in the Bible but not expressly articulated. The Catholic Church thinks Jesus has given authority to the Church to articulate these things. These are articulated slowly and carefully as the Church marches through time on its “Pilgrimage of Faith.” Both Catholics and Evangelicals agree that no spiritual truth will conflict with the Bible. Amen to that.
Some Evangelicals claim that Deut 18:10-12 rails against the concept of Purgatory and praying for the dead. The Church feels there is an important distinction between Deut 18:10-12 and Purgatory. Catholics pray
for the dead -not
to them. I would pray
for you but I would not pray
to you.
Catholics believe there is enough evidence of Purgatory in Scripture to validate its existence. Evangelicals would agree that even if there is one instance of a spiritual principle in the Bible, then it is true because the Bible is the embodiment of Truth.
Paul prayed for Onesiphorous after he died, “may the Lord grant that he
will find mercy from the lord on that day” (2nd Timothy 1:16-18).
“After his death, Jesus went to preach to the Spirits in prison” (1 Pet 3:19)
“Nothing unclean can enter heaven” (Rev 21:27)
Catholics believe Jesus speaks of purgatory in Matthew 18:23-35. He says: “The kingdom of heaven may be likened to…” and then He tells a story about a king who forgave a servant’s large debt. That same servant refused to forgive a much smaller amount of a fellow servant. The king then threw the first servant into prison “until he should pay back the whole debt.” Jesus then says, “So will my Heavenly Father do to you, unless each of you forgives his brother from his heart.” Catholics feel the prison in the Kingdom of Heaven where one might remain until the debt is satisfied is Purgatory.
Catholics believe Paul also spoke of purgatory:
“The work of each will come to light, for the day will disclose it. It will be revealed with fire, and the fire [itself] will test the quality of each one’s work. If the work stands that someone built upon the foundation, that person will receive a wage. But if someone’s work is burned up, that one will suffer loss, the person will be saved, but only as through fire.” (1 Corinthians 3:11-15)
The church is says:
Pray ***for ***the souls in Purgatory
Ask Angels, Saints and Mary to pray ***for ***us
Pray ***to ***Jesus
Biblical passages that Catholics feel refer to Purgatory
Ps 66:12, Mt 12:32, Phil 2:10-11, Ecc 12:14, Lk 16:19-31, 1 Thess 3:13, Is 4:4 (cf. Eph 4:8-10; 4:7 6:5-7 1 Pet 3:19-20) 2 Tim 1:16-18, Mic 7:8-9, 1 Cor 3:11-15, Heb 12:14, Mal 3:1-4 15:29 12:29, 2 Maccabees 12:39-45, 2 Cor 5:10, Rev 5:3,13, Mt 5:25-6, Lk 12:58-9, 7:1, 21:27
You wanted documentation. 
