Your question is based on an unsupported assumption. It begs the following question. Must everything Christians do be found in Scripture? The answer is no. That answer can even be found in Scripture:
2 Thessalonians 2:15Regardless of the fact that your principle is wrong and contrary to scripture, here is a good answer from James Akin:So then, brothers, stand firm and hold to the teachings[ 2:15 Or traditions] we passed on to you, whether by word of mouth or by letter.
A: Well, aside from the fact that the Magisterium has ruled on the issue and that Apostolic Tradition teaches it (both of which are sufficient to prove the matter), the Bible also teaches it.Regarding Luther's non-biblical doctrine of "sola Scriptura," the passage that you're thinking of citing from the book of Revelation refers only to the book of Revelation. That's the book that John was writing. John couldn't have been referring to what we now know as the Bible because the Bible wasn't to be canonized for another 400 years. And then that canon was the one including the above passage, not Luther's abridged version. By what authority did Luther remove books from the Bible? Where in the Bible is Luther directed to remove books from the Bible?In the book of Psalms, which was the hymn book for the Temple in Jerusalem, we sing to those in the heavenly court and exhort them:
"Bless the Lord, O you his angels, you mighty ones who do his word, hearkening to the voice of his word! Bless the Lord, all his hosts, his ministers that do his will!" (Psalm 103:20-21, RSV, as below)The fact that those in the heavenly court can hear our prayers is also indicated in the book of Revelation, where we read:
"And another angel came and stood at the altar with a golden censer; and he was given much incense to mingle with the prayers of all the saints upon the golden altar before the throne; and the smoke of the incense rose with the prayers of the saints from the hand of the angel before God." (Revelation 8:3-4)Thus those saints who are angels have a role in presenting our prayers to God in an intercessory manner. (Angels are also saints, as indicated by the fact that the Bible applies the Hebrew word for saint/holy one -- qaddiysh -- to them, cf. Daniel 4:13, 23, 8:13. Thus we speak of St. Michael the Archangel, St. Gabriel, St. Raphael, etc.).
Since the Ascension of Christ, when Jesus took the Old Testament saints from sheol to heaven, large numbers of humans saints have also been in heaven, and Revelation indicates they also present our prayers to God:
"And when he [the Lamb] had taken the scroll, the four living creatures and the twenty-four elders fell down before the Lamb, each holding a harp, and with golden bowls full of incense, which are the prayers of the saints" (Revelation 5:8).The twenty-four elders represent the hierarchy of the people of God in heaven (just as the four living creatures represent the hierarchy of the angels of God in heaven), and here they are shown presenting our prayers to God under the symbol of incense (which is, in fact, what incense symbolizes in church, since it is a pleasing smell which rises upward).
One might object, saying, "But maybe those weren't prayers to the saints but prayers to God!" This may well be true. However, a person who says this only digs the hole deeper for himself since this would mean that those in heaven are aware of prayers which weren't even directed to them!
In any event, we know that the saints in heaven (whether human saints or angel saints) are aware of our prayers and, based on them, intercede with God on our behalf. Scripture, Tradition, and the Magisterium all agree.