If you are searching for any particular guideline or rules of conduct this is about as close as I can come.
In Druidry, the virtue of telling the truth reigns supreme. In the lore I have read, if a Druid of old told an untruth it would make their cause fail and could cause their death. The only thing that would set it right was speaking
fir flathemon.
Concepts of Truth and SovereigntyAn Fhirinne in aghaidh an tSaoil translates too
The Truth Facing The World and
fir flathemon means
The Truth of Sovereignty.
In one story King Lugaid gives a false judgement, the courthouse begins to fall. When Cormac Mac Airt gives the correct judgement and the people cry out "This is the Truth!" The truth then, magickally restores the courthouse and Cormac becomes sovereign. He becomes king, not as a reward of virtue, but because of a magickal transfer of power to a right and just source.
One thing to keep in mind here is that when there is an appearance of a king or queen in celtic myth it symbolizes our divine Self, the true and Sovereign inner Self. It is important to remember this because acting from your inner truth has magickal power.
The Truth of Sovereignty puts an enormous responsibility on each of our shoulders. We have no external God keeping an eye on us, we have no church laws ordering how we should act: we each, are responsibile for our actions and have to live with the consequences, but we do have the Goddess within us and the Goddess of the Land.
I gained a lot of this knowledge and information from this book
I would highly recommend it too anybody starting down this path 
