Where in known fiction entailing magic—including written and oral forms predating the novel—did the concept of a magical sword first appear? Answers should clearly distinguish between any magic of the wielder and the magic of the sword itself.
Clarification: In response to a point made in chat by @Axelrod, I am using the "history-of" tag because I am interested in the history of the idea or trope of the magic sword, not in any history of actual magic swords.
The sword Asi, the first sword ever created, was supposedly made by Brahma (the creator of the universe in the Mahabharata) in a fire sacrifice ritual next to the Himalaya, as a tool for the Devas to fight back against the Asuras. It was a sentient weapon, derived from a being described in section CLXVI:
His complexion was dark like that of the petals of the blue lotus. His teeth were keen. His stomach was lean. His stature was tall. He seemed to be irresistible and possessed of exceeding energy. Upon the appearance of that being, the earth trembled.
That (clearly magical) being then turned into a sword:
That being then, abandoning the form he had first assumed, took the shape of a sword of great splendour, highly polished, sharp-edged, risen like the all-destructive Being at the end of the Yuga.
The Mahabharata itself dates from 400 BC, but the epic form it was based on appears to have an origin around the 9th century BC. That places it at roughly 1800 years older than Beowulf.
There are almost certainly much older examples, but this was the one I first thought of- slightly older than the stories of Excalibur:
The sword Beowulf uses to kill Grendel's mother.
According to wikipedia:
c. 700–1000 CE (date of poem), c. 975–1010 CE (date of manuscript)
As readable on Project Gutenburg (chapters XXIII - XXIV), Beowulf goes to slay Grendel's mother, but discovers that his (normal) sword was not powerful enough to harm the monster.
(XXIII 48-54)
The stranger perceived then
The sword will not bite.
The sword would not bite, her life would not injure,
But the falchion failed the folk-prince when straitened:
Erst had it often onsets encountered,
Oft cloven the helmet, the fated one’s armor:
’Twas the first time that ever the excellent jewel
Had failed of its fame.
Beowulf despairs and tries to fight her without his sword, and is protected from her dagger by his armour, and would have died "had God most holy not awarded the victory"
(XXIII 75-82)
Ecgtheow’s son there
Had fatally journeyed, champion of Geatmen,
In the arms of the ocean, had the armor not given,
Close-woven corslet, comfort and succor,
God arranged for his escape.
And had God most holy not awarded the victory,
All-knowing Lord; easily did heaven’s
Ruler most righteous arrange it with justice;
Uprose he erect ready for battle. (End of Chapter)
He then sees (delivered through divine intervention/deus ex machina?) a giant and magical (?) sword, more powerful than his own (very high quality yet not magical) sword and successfully uses it to penetrate the monster's skin and kill her.
(XXIV 1-6)
Then he saw mid the war-gems a weapon of victory,
An ancient giant-sword, of edges a-doughty,
Glory of warriors: of weapons ’twas choicest,
Only ’twas larger than any man else was
Able to bear to the battle-encounter,
The good and splendid work of the giants.
Extra, fun note: her blood was so hot and poisonous that it dissolves the blade of the giant sword, and Beowulf can only bring the hilt back.
(XIV 57-59)
The brand early melted, burnt was the weapon:
So hot was the blood, the strange-spirit poisonous
The hero swims back to the realms of day.
That in it did perish
It is debatable whether the giant sword is actually "magical" or just giant, but on later inspection later in the book, it is definitely supernatural-not made by normal humans and possessing a greater power than normal humans could have infused it with.
(XXV 26-47)
To the age-hoary man then,
The famous sword is presented to Hrothgar.
The gray-haired chieftain, the gold-fashioned sword-hilt,
Old-work of giants, was thereupon given;
Since the fall of the fiends, it fell to the keeping
Of the wielder of Danemen, the wonder-smith’s labor,
And the bad-mooded being abandoned this world then,
Opponent of God, victim of murder,
And also his mother; it went to the keeping
Of the best of the world-kings, where waters encircle,
Who the scot divided in Scylding dominion.
Hrothgar discoursed, the hilt he regarded,
The ancient heirloom where an old-time contention’s
Beginning was graven: the gurgling currents,
The flood slew thereafter the race of the giants,
They had proved themselves daring: that people was loth to
The Lord everlasting, through lash of the billows
The Father gave them final requital.
So in letters of rune on the clasp of the handle
Gleaming and golden, ’twas graven exactly,
Set forth and said, whom that sword had been made for,
Finest of irons, who first it was wrought for,
Wreathed at its handle and gleaming with serpents.
I can beat Asi by 2599 years with a fairly boring answer.
Wikipedia states (without citation) that "It is probable that the roots of the sentient weapon myths stem from ancient peoples belief that sword making and metallurgy was in fact a magical process."
This is reinforced by claims made in this paper (top of page 9), which seems to know what it is talking about and states that people of the time thought that metallurgy was magic - that is, any sword made of metal, is magic.
That means, that we are looking for the first story, written or oral, that contains a metal sword, which likely dates from several months or years after the invention of the sword, in roughly 3100 BC. That is to say, in the minds of the author and reader (or speaker and listener), the swords they describe are magical, even if you and I wouldn't think of them as magical in the sense of glowing when Orcs are present.
Unfortunately, that means that almost certainly, the first story of a magical sword is no longer remembered or recorded, same for the 2nd oldest, hundredth oldest and so on. This question is unanswerable.
Earliest I know of is Genesis 3.24 - God places an angel with a flaming sword at the gates to the Garden of Eden. The Mahabarata example seems like a better bet.
