“There is a saying: Yesterday is History; Tomorrow is a Mystery; but Today is a Gift. That is why it is called the Present.” Master Oogway
While unable to find the original source, most web searches attribute the quote to Alice Morse Earle as “The clock is running. Make the most of today. Time waits for no man. Yesterday is history. Tomorrow is a mystery. Today is a gift. That’s why it is called the present.” and reference the book Sun dials and roses of yesterday. While the book contains many interesting Sun-dial mottoes, nothing exactly matches. I found this one from her book apropos:
TYME PASSETH AND SPEAKETH NOT,
DETH COMETH AND WARNETH NOT,
AMENDE TODAY AND SLACK NOT,
TOMORROW THYSELF CANNOT.