Like bitcoin, the Quran represents an immutable ledger of verses that has been preserved through time by recitation among most adherents in its original language. Compare a Quran from Russia to a Quran from India and you will get the same exact Arabic text. Compare the Quran today to the Quran 1400 years ago and you will get the same Arabic text.
For those of you who don't know the Holy Quran is the indisputable scripture of Muslims worldwide. While disagreements on how to interpret certain verses in the Quran do exist the original Quran has been preserved letter by letter, verse by verse throughout time exclusively in the Arabic language. A Shia Muslim and Sunni Muslim would agree on the same book. A Muslim from China and a Muslim from Brazil will agree on the original Arabic recitation of the Quran because regardless of the local language they must memorize the Quran in it's original Arabic. This makes Islam different from other religions in that it's central scripture was distributed widely and not concentrated in the hands of just a few people. It remains the only religious text widely disseminated in it's original language and memorized word for word by its adherents.
The Quran was always meant to be recited instead of written and read. The very word Quran is derived from the Arabic root word for recitation. Muslims believe the Prophet Muhammad got these verses revealed to him directly by God and then recited it to the people who then memorized it and recited it to others who would do the same. The very first verses that were revealed to the Prophet can be regarded as the genesis block. Eventually the Quran was written down to preserve it, but the primary way it spread was through recitation since most of the Arab population was illiterate at the time. The Prophet would recite it to his earliest followers (the Sahabaa) and they would then recite it to their friends and family and so on. The question arises that once the Prophet received the verses from God, what would stop others who the Prophet recited these verses to to change them? What would stop someone from altering a few words to favor their family or businesses? The answer is the mandate of congregational prayer:
Muslims are required to pray 5 times a day, every day either in private or in a congregation of other Muslims with the exception of the holy day of Friday where all Muslims must congregate and pray. In the congregation there is a prayer leader who will recite verses from the Quran out loud in Arabic while all the other congregants stand behind him (the amount of congregants standing behind can range from the single digits to the tens of thousands for a single prayer leader). As he is reciting verses from the Quran out loud from memory while all other Muslims behind him listen. If he is wrong in even one letter of one word he is corrected by others standing behind him who have memorized the same text and this correction relies on the consensus of all the others in congregation who will approve of that correction by staying silent or speaking up on their own. It's a beautiful system that works to preserve the original integrity of the holy verses. This is similar to the hashing functions chosen miners do to solve the block while all the other nodes verify their work and make sure the work stays immutable and decentralized. If a hacker seeks to change the ledger, he/she changes the hash which will immediately rejected by all other nodes in the system who have memorized a different hash in their ledgers.
Now, what if the majority of people get together and agree to change the verses? This is known as the 51% attack and presents as a problem in the proof of work algorithm of both Bitcoin and the Holy Quran. How does bitcoin solve this? Through immense decentralization and an increase in required hashing power as more people join the system so no one person can possibly have enough hashing power to change the ledger. The Holy Quran is protected by a similar mechanism: the immense diversity and worldwide spread of the Quran makes it virtually impossible to change the text because of massive worldwide distributed consensus: the vest majority of Muslims will memorize at least a few Quranic verses by heart and some will memorize the entire text, these Muslims are called hufaaz (arabic for Protector) and they are spread throughout the planet.
I know this isn't a one to one comparison and many of you may see this as just promoting a positive aspect of a religion while ignoring the negatives but it's hard to dispute that both Bitcoin and Quran represent immutable ledgers that have intrinsic mechanisms in place within their communal systems to stay immutable.