The Surangama Sutra: The Four Clear and Unalterable Instructions on Purity - Refrain from Stealing and Lying, Part 5 of 7, Dec. 23, 2018

That’s the most heinous lie of all, that you say you attained Buddhahood, but you have not. Meaning deceiving other beings, and then the other beings, they follow you, they also fall into the same pit. That is why it is so bad. This is the worst lie you can commit, because you lead other beings into the false views with you too, believing in your power, when you don’t have it. So, if you go to hell, they will have to go with you, because you deceived them. Also, deprived them from a chance to meet a real living Buddha, and that’s why it’s the worst sin you can commit, the worst lie ever. In Buddhism, they say it’s the greatest lie that you can commit, unredeemable.