Faint outlines of a Bible passage were recently discovered on an ancient Quran manuscript, making it “the only recorded palimpsest in which a Christian text has been effaced to make way for the Islamic holy text,” according to The Guardian.

French scholar Eleonore Cellard discovered that there was a faint manuscript of the Bible behind the ancient Quran text when she looked at an image of the eighth century Quran, which was sold by Christie’s Auction House 10 years ago.

During her examination of the photos, she said she noticed faint Coptic letters behind the Arabic script. She contacted Christie’s to let them know what she saw.

Together, the two parties discovered that the faint Coptic writing came from the Book of Deuteronomy, which is a part of the Torah and the Christian Old Testament.

“This is a very important discovery for the history of the Quran and early Islam. We have here a witness of cultural interactions between different religious communities,” Cellard said, according to The Guardian.

Christie’s, which is selling the manuscript piece at an auction for £80,000 to £120,000 ($111,549 to $167,323 USD), said the piece of paper likely came from Egypt, which still used the Coptic language during the Arab conquest, according to Arab News.

Christie’s specialist Romain Pingannaud said that the Coptic writing likely came around the seventh century, but it’s hard to determine the precise timeline.

“It’s quite extraordinary,” said Pingannaud. “Once you know it’s there, you can only see it, it becomes so obvious. We missed it at the beginning. It’s fascinating, particularly because it’s the only example where you have an Arabic text on top of a non-Arabic text. And what’s even more fascinating is it is on top of passages from the Old Testament. … It shows the contact between communities in the first centuries of Islam; it’s very relevant.”

As Hawzah News reported, the palimpsest is only one of a handful ever recorded in history (though this is the first with Christian text written on a Quran manuscript). In 2008, for example, a Hijazi Quran written in the seventh century was copied on top of an earlier text from the Quran.