0856 (pre): Black Dog Searches Church
The earliest recorded sighting of a black dog is in a French manuscript ― Annales Franorum Regnum ― dating from 856 CE, and tells how a provincial church was suddenly enveloped in darkness, during which time a large black dog with glowing eyes appeared, searched about the church quickly, then vanished.
I've searched high and low for the Annales Franorum Regnum, and have found no evidence for its existence. I didn't expect to get my hands on a copy, mind you; but there should be some record as to who owns and protects a manuscript that is over a thousand years old, and there just isn't in this case.
The earliest I've found any reference to this manuscript is just 1990, in a FATE Magazine article on Black Dogs written by a man named Gordon Stein... and it's from this article that all other references to the Annales Franorum Regnum stem from. But Stein doesn't say where he actually saw this manuscript, if he did.
I say if not only because I can't find an earlier record for the manuscript, but because of a basic flaw that Stein made and that everyone else repeated... you see, Annales Franorum Regnum isn't French; it's Latin. It translates as "Annals Frans Kingdom," which also doesn't seem to relate to anything now or historically. So the title itself appears to have been made up.
So, despite the nice claim of being the earliest recorded instance of a Black Dog encounter, I have to consider this to be a false lead until such a time as a copy of the proposed manuscript is actually produced.