Sefarim are sometimes censored for various reasons. It used to be mostly external censorship, but nowadays I think it is mostly internal censorship.
When people print sefarim and censor them, they often get called out on it by others. There are a number of blogs where one can find plenty of accusations of censorship of sefarim in recent times.
However, we don't often find the accusations themselves in rabbinic literature. I am looking for early sources in rabbinic literature that accused others of censoring sefarim. The earliest accusation that I have seen thus far is by R. Yehuda Aryeh Modena:
הסכת ושמע ישראל באזנים קשובות הקיות ועיונית מה שכתב בעל ספר יוחסין דפוס קושטנטינא כי בדפוס קראקא נשמט אולי להפקת רצון איזה אחד מכת המקובלים פן תגלה האמת לעולם
Here he suggests that an anti-Zohar passage was removed from the Krakow edition of Sefer Yuchasin, perhaps because the kabbalists were afraid that it would show the world the truth.
Does anyone know of any earlier examples?
For reference, the book cited above was completed in December 1628, so I'm looking for examples prior to that.