Le Morte D'Arthur

So he departed from him with Sir Driant, and by the way they met with a knight that was sent from Morgan le Fay unto King Arthur; and this knight had a fair horn harnessed with gold, and the horn had such a virtue that there might no lady nor gentlewoman drink of that horn but if she were true to her husband, and if she were false she should spill all the drink, and if she were true to her lord she might drink peaceable. And because of the Queen Guenever, and in the despite of Sir Launcelot, this horn was sent unto King Arthur; and by force Sir Lamorak made that knight to tell all the cause why he bare that horn. Now shalt thou bear this horn, said Lamorak, unto King Mark, or else choose thou to die for it; for I tell thee plainly, in despite and reproof of Sir Tristram thou shalt bear that horn unto King Mark, his uncle, and say thou to him that I sent it him for to assay his lady, and if she be true to him he shall prove her. So the knight went his way unto King Mark, and brought him that rich horn, and said that Sir Lamorak sent it him, and thereto he told him the virtue of that horn. Then the king made Queen Isoud to drink thereof, and an hundred ladies, and there were but four ladies of all those that drank clean. Alas, said King Mark, this is a great despite, and sware a great oath that she should be burnt and the other ladies.

Then the barons gathered them together, and said plainly they would not have those ladies burnt for an horn made by sorcery, that came from as false a sorceress and witch as then was living. For that horn did never good, but caused strife and debate, and always in her days she had been an enemy to all true lovers. So there were many knights made their avow, an ever they met with Morgan le Fay, that they would show her short courtesy. Also Sir Tristram was passing wroth that Sir Lamorak sent that horn unto King Mark, for well he knew that it was done in the despite of him. And therefore he thought to quite Sir Lamorak.