Thomas Malory's book "Le Morte D'Arthur" is the most famous account of King Arthur's life. It begins with the story of how Arthur's father Uther Pendragon desired Igrayne, the wife of the Duke of Cornwall. So he asked the wizard Merlin to make him look like the Duke of Cornwall, so he could trick Igrayne. Merlin agreed, on the condition that the child produced from their union be given to him. The child produced was Arthur, and Merlin gave the child to Sir Ector to raise. Then after Uther's death, Arthur pulled a sword from a stone and thereby became king of England.
Now as I said Malory's book relates all this, but Geoffrey of Monmouth's "History of the Kings of Britain", which is the earliest work mentioning the above story of Uther and Igrayne, does not mention Arthur being raised by Sir Ector or pulling out a sword from the stone. Here is all it says:
Uther Pendragon being dead, the nobility from several provinces assembled together at Silcestre, and proposed to Dubricius, archbishop of Legions, that he should consecrate Arthur, Uther's son, to be their king. For they were now in great straits, because, upon hearing of the king's death, the Saxons had invited over their countrymen from Germany, and, under the command of Colgrin, were attempting to exterminate the whole British race. They had also entirely subdued all that part of the island which extends from the. Humber to the sea of Cathness. Dubricius, therefore, grieving for the calamities of his country, in conjunction with the other bishops, set the crown upon Arthur's head. Arthur was then fifteen years old, but a youth of such unparalleled courage and generosity, joined with that sweetness of temper and innate goodness, as gained him universal love.
So my question is, what is the earliest reference to King Arthur being raised by Sir Ector?