The Fountain of Pity and Mercy, The Miraculous Fountain
In Chrétien’s Le Chevalier au Lion, Yvain (Ywaine) encounters a marvelous fountain situated at the foot of an olive tree. This fountain is described as having the extraordinary ability to change color five times a day. Each change of color corresponds to a different mystical property or effect.
As Yvain approaches the fountain, he encounters a damsel who explains the significance of the changing colors. She informs Yvain that any knight who drinks from the fountain and engages in a battle within the following ten days will experience enhanced strength and prowess during the fight. However, the damsel also warns that a knight who drinks from the fountain must be prepared to face a fierce and worthy opponent in combat.
Yvain, intrigued by the fountain’s magical properties, decides to drink from it. He then encounters the Red Knight, a formidable adversary, in a battle that tests his newfound strength and skill.
Source
Yvain, or Le Chevalier au Lion | Chrétien de Troyes, late 12th century