At this moment her thoughts were interrupted by a loud shouting of 'Ahoy! Ahoy! Check!' and a Knight dressed in crimson armour came galloping down upon her, brandishing a great club. Just as he reached her, the horse stopped suddenly: 'You're my prisoner!' the Knight cried, as he tumbled off his horse.
Startled as she was, Alice was more frightened for him than for herself at the moment, and watched him with some anxiety as he mounted again. As soon as he was comfortably in the saddle, he began once more 'You're my—' but here another voice broke in 'Ahoy! Ahoy! Check!' and Alice looked round in some surprise for the new enemy.
This time it was a White Knight. He drew up at Alice's side, and tumbled off his horse just as the Red Knight had done: then he got on again, and the two Knights sat and looked at each other for some time without speaking. Alice looked from one to the other in some bewilderment.

Through the Looking Glass (And What Alice Found There), Chapter 8 - "It's my own Invention"