No written writings from authority, just from literature considered heresy (Written CENTURIES after the fact) by your own church fathers/Popes. Clement of Rome, Ignatius, Tertullian, Irenaeus, Melito, Cyprian, Athanasius, Augustine, Theodoriet, Cyril of Jerusalem, Chrysostom all closer to the times never mentioned/taught about an assumption of Mary. But 1800-1900 years later from their time it is know considered damnable. Yeah right.
Just to be clear, that's *one* book, which contained lots of fanciful stuff in addition to the Assumption, and its condemnation specified nothing about any erroneous doctrines in it, but only that it was "written and used by heretics".
It isn't the only source for the dogma, or the main one, or necessarily even the earliest one.