Who said "Today, beat the person you were yesterday."?

Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Water (closing).

What is the original Japanese?

今日は昨日の我に勝ち、あすは下手に勝ち、後は上手に勝と思ひ. Translated from the original Japanese by Spartan Surfers.

Today, beat the person you were yesterday.

Miyamoto Musashi, The Book of Five Rings, Water (closing)

The source

"Today, beat the person you were yesterday." Miyamoto Musashi said it in The Book of Five Rings, Water (closing). Translated from the original Japanese by Spartan Surfers.

"今日は昨日の我に勝ち、あすは下手に勝ち、後は上手に勝と思ひ"

Original Japanese, The Book of Five Rings, Water (closing). Japanese: Miyamoto Musashi (Kinkodo, 1909), NDL digital text.

Who said it

Miyamoto Musashi (c. 1584–1645). Undefeated swordsman who wrote The Book of Five Rings in a cave a few weeks before he died.

Questions

Who said "Today, beat the person you were yesterday."?: Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Water (closing).
What is the original Japanese?: 今日は昨日の我に勝ち、あすは下手に勝ち、後は上手に勝と思ひ. Translated from the original Japanese by Spartan Surfers.