The Dead Sea Scrolls
Lawrence H. Schiffman, Texts and Traditions, Ktav, Hoboken 1998, p.517-518.
The traditions of the fathers, or elders, mentioned by Josephus, are an important component of what the Rabbis later called oral law. The traditions were a hallmark of the Pharisaic approach to Torah and continued into Rabbinic tradition as it was later enshrined in the Mishnah.
(297) …What I would now explain is this, that the Pharisees have passed on to the people a great many observances handed down by their fathers, which are not written down in the law of Moses. For this reason the Sadducees reject them and say that we are to consider to be obligatory only those observances which are in the written word, but need not observe those which are derived from the tradition of our forefathers.