Sir Thomas Malory 
Le Mort d’Arthur: Volume 2 [EPUB ebook] 

BOOK X
CHAPTER I. How Sir Tristram jousted, and smote down King Arthur, because he told him not the cause why he bare that shield.
AND if so be ye can descrive what ye bear, ye are worthy to bear the arms. As for that, said Sir Tristram, I will answer you; this shield was given me, not desired, of Queen Morgan le Fay; and as for me, I can not descrive these arms, for it is no point of my charge, and yet I trust to God to bear them with worship. Truly, said King Arthur, ye ought not to bear none arms but if ye wist what ye bear: but I pray you tell me your name. To what intent? said Sir Tristram. For I would wit, said Arthur. Sir, ye shall not wit as at this time. Then shall ye and I do battle together, said King Arthur. Why, said Sir Tristram, will ye do battle with me but if I tell you my name? and that little needeth you an ye were a man of worship, for ye have seen me this day have had great travail, and therefore ye are a villainous knight to ask battle of me, considering my great travail; howbeit I will not fail you, and have ye no doubt that I fear not you; though you think you have me at a great advantage yet shall I right well endure you. And there withal King Arthur dressed his shield and his spear, and Sir Tristram against him, and they came so eagerly together. And there King Arthur brake his spear all to pieces upon Sir Tristram's shield. But Sir Tristram hit Arthur again, that horse and man fell to the earth. And there was King Arthur wounded on the left side, a great wound and a perilous.
Then when Sir Uwaine saw his lord Arthur lie on the ground sore wounded, he was passing heavy. And then he dressed his shield and his spear, and cried aloud unto Sir Tristram and said: Knight, defend thee. So they came together as thunder, and Sir Uwaine brised his spear all to pieces upon Sir Tristram's shield, and Sir Tristram smote him harder and sorer, with such a might that he bare him clean out of his saddle to the earth. With that Sir Tristram turned about and said: Fair knights, I had no need to joust with you, for I have had enough to do this day. Then arose Arthur and went to Sir Uwaine, and said to Sir Tristram: We have as we have deserved, for through our orgulyté we demanded battle of you, and yet we knew not your name. Nevertheless, by Saint Cross, said Sir Uwaine, he is a strong knight at mine advice as any is now living.