Who said "Masters look unhurried, yet never miss a beat."?

Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Wind (Speed in Other Schools).

What is the original Japanese?

上手のする事は、緩々と見えて間のぬけざる所也. Translated from the original Japanese by Spartan Surfers.

Masters look unhurried, yet never miss a beat.

Miyamoto Musashi, The Book of Five Rings, Wind (Speed in Other Schools)

The source

"Masters look unhurried, yet never miss a beat." Miyamoto Musashi said it in The Book of Five Rings, Wind (Speed in Other Schools). Translated from the original Japanese by Spartan Surfers.

"上手のする事は、緩々と見えて間のぬけざる所也"

Original Japanese, The Book of Five Rings, Wind (Speed in Other Schools). 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 "Masters look unhurried, yet never miss a beat."?: Miyamoto Musashi (c. 1584–1645). Source: The Book of Five Rings, Wind (Speed in Other Schools).
What is the original Japanese?: 上手のする事は、緩々と見えて間のぬけざる所也. Translated from the original Japanese by Spartan Surfers.