Looking for evidence of Rabbinic law in Tanakh

At shabbos lunch a few weeks ago I got into a discussion with my friend about the definition of Torah she'b'al peh (oral law).  I said that there is no mention in Tanakh of any thing pertaining to oral law or things that could be construed as examples of "rabbinic" law - that is- an observance though not in the written Torah but which could be recognized as coming from a body of unwritten law or tradition.  Well, It turns out I spoke too soon.  In doing a quick scan of Tanakh I have found two or three instances of observance not recorded in the Torah. 

     Daniel 1:8 records that Daniel and his friends would not eat the king's food or drink his wine.  A prohibition against wine of a gentile would be part of a nonwritten tradition later codified in the Talmud.  Similarly Daniel 6:11 tells of Daniel praying toward Jerusalem three times a day- certainly a later post Torah development.

     In Nechemiah 10:35 lots are drawn among the cohanim and leviim for the privilege of bringing the sacrifices.  Although this procedure is mentioned in the Gemara it may just be a natural way for the fledgling community to deal with mismatch in the number of cohanim and leviim vs. the number of korbanot.  Similarly a prohibition of selling grain on the New Moon is implied in Amos 8:5.  If this is an example of a nonTorah tradition it would be the only one I find in all of the preexilic Tanakh. More likely there was a semi holiday associated with rosh chodesh during first temple times (see 2Kings 4:23  and 1Samuel 20:18-27).  In any event the prohibition of labor on rosh chodesh never made it in final form into talmudic law.
      Most scholars regard Daniel as postexilic in its final form (around 164 BCE) and certainly Nechemiah is postexilic.  So it seems that whatever evidence of oral law exists in Tanakh appears only in the latest books of the Bible

     Although it is not my purpose to show examples of observance that run contrary to oral law in our present day iteration in this short post, I will mention just a few examples on which I plan to elaborate in a later article.  Nechemiah 13:23 states the prohibition of marrying an Ammonitess or Moabitess.  Ezra 2:65 regarding singing women which is a later Rabbinic prohibition.  Both the books of Ezra and Nechemiah pertray the Leviim as active participants in the Golah community even though the Talmud in Yevamot speaks of Ezra penalizing the Leviim for not accompanying him on the trip from Babylonia.   In  Maccabees 1:38-41 lifting the ban on self defense on the Sabbath both point to a oral tradition which was still fluid in post exilic times.

     If there are instances of oral tradition in Tanakh or in the second temple period apocryphal books that I have missed I would appreciate your input.