Ful sooth is seyd that love ne lordshipe
Wol noght, his thankes, have no felaweshipe.
Modern English:
Well is it said that neither love nor power
Admit a rival, even for an hour.
– Geoffrey Chaucer
The Canterbury Tales, The Knight’s Tale. The Knight says that neither love nor power will admit a rival and both Arcite and Palamon will soon find that to be true. This is after the two love rivals agree to fight a duel for the hand of Emily.