The Anglo-Saxon Chronicle, 1002
The king that is mentioned below is King Æthelred The Unready—a Pythonesque sobriquet for an ineffectual monarch. More details on him here.
From the Chronicle:
This year the king and his council agreed that ribute should be given to the fleet, and peace made with them, with the provision that they should desist from their mischief. Then sent the king to the fleet Alderman Leofsy, who at the king’s word and his council made peace with them, on condition that they received food and tribute; which they accepted, and a tribute was paid of 24,000 pounds. In the meantime Alderman Leofsy slew Eafy, high-steward of the king; and the king banished him from the land. Then, in the same Lent, came the Lady Elfgive Emma, Richard’s daughter, to this land. And in the same summer died Archbishop Eadulf; and also, in the same year the king gave an order to slay all the Danes that were in England. This was accordingly done on the mass-day of St. Brice; because it was told the king, that they would beshrew him of his life, and afterwards all his council, and then have his kingdom without any resistance.
A particularly gruesome massacre took place at St Frideswide’s church on St. Brice’s day, November 13th, at the location where Christ Church Cathedral now stands in Oxford. The Danish community attempted to take refuge there, but the citizens burned down the church, killing most inside. More details can be found here.
The king’s “purpose” was to drive the Dane’s out of England, but it thoroughly backfired as they became so enraged that it led to a massive invasion the following year.