Book IX - Chapter XXX - How Sir Tristram behaved him the first day of the tournament, and there he had the prize.
NOW turn we unto Sir Tristram de Liones, that commanded Gouvernail, his servant, to ordain him a black shield with none other remembrance therein. And so Sir Persides and Sir Tristram departed from their host Sir Pellounes, and they rode early toward the tournament, and then they drew them to King Carados' side, of Scotland; and anon knights began the field what of King Northgalis' part, and what of King Carados' part, and there began great party. Then there was hurling and rashing. Right so came in Sir Persides and Sir Tristram and so they did fare that they put the King of Northgalis aback. Then came in Sir Bleoberis de Ganis and Sir Gaheris with them of Northgalis, and then was Sir Persides smitten down and almost slain, for more than forty horse men went over him. For Sir Bleoberis did great deeds of arms, and Sir Gaheris failed him not. When Sir Tristram beheld them, and saw them do such deeds of arms, he marvelled what they were. Also Sir Tristram thought shame that Sir Persides was so done to; and then he gat a great spear in his hand, and then he rode to Sir Gaheris and smote him down from his horse. And then was Sir Bleoberis wroth, and gat a spear and rode against Sir Tristram in great ire; and there Sir Tristram met with him, and smote Sir Bleoberis from his horse So then the King with the Hundred Knights was wroth, and he horsed Sir Bleoberis and Sir Gaheris again, and there began a great medley; and ever Sir Tristram held them passing short, and ever Sir Bleoberis was passing busy upon Sir Tristram; and there came Sir Dinadan against Sir Tristram, and Sir Tristram gave him such a buffet that he swooned in his saddle. Then anon Sir Dinadan came to Sir Tristram and said: Sir, I know thee better than thou weenest; but here I promise thee my troth I will never come against thee more, for I promise thee that sword of thine shall never come on mine helm.
With that came Sir Bleoberis, and Sir Tristram gave him such a buffet that down he laid his head; and then he caught him so sore by the helm that he pulled him under his horse's feet. And then King Arthur blew to lodging. Then Sir Tristram departed to his pavilion, and Sir Dinadan rode with him; and Sir Persides and King Arthur then, and the kings upon both parties, marvelled what knight that was with the black shield. Many said their advice, and some knew him for Sir Tristram, and held their peace and would nought say. So that first day King Arthur, and all the kings and lords that were judges, gave Sir Tristram the prize; howbeit they knew him not, but named him the Knight with the Black Shield.