“Four things come not back: the broken word, the spent arrow, the past life, and the neglected opportunity” was cited in print in 1870. “There are three things that return not: the spoken word, the spent arrow, and the lost opportunity!” was cited in print in 1875, when it was called an Arab proverb. Umar/Omar (577-644) is frequently credited.
   
The proverb has also been credited as Chinese.
 
   
23 September 1870, The Jewish Messenger (New York, NY), “Floating Facts,” pg. 8, col. 5:
Four things come not back: the broken word, the spent arrow, the past life, and the neglected opportunity.
 
Chronicling America
2 November 1870, Juanita Sentinel (Mifflintown, PA), pg. 2, col. 3:
Four things come not back: the broken word, the spent arrow, the past life, and the neglected opportunity.
   
Google Books
April 1875, Atlantic Monthly, pg. 413:
... the next page, but there is no proverb truer than that of the Arab, “There are three things that return not: the spoken word, the spent arrow, and the lost opportunity!”
     
Google Books
24 October 1896, The Speaker, pg. 439, col. 1:
“Three things come not back,” said the Caliph Omar—“the spent arrow, the spoken word, and the lost opportunity.”
 
Google Books
The Life of Isabella Bird (Mrs. Bishop)
By Anna M. Stoddart
London: John Murray
1906
Pg. 330:
... it was from Seoul that she sent out the New Year’s card on which she quotes the ancient Persian proverb of “Three things that never return”:
 
The Spent Arrow,
The Spoken Word,
The Lost Opportunity.
 
27 September 1907, San Diego (CA) Union, pg. 5, col. 4 ad:
The wise Omar said: “Three things never come back, the spoken word, the spent arrow, and the lost opportunity.” It does not take an Omar to see the opportunities now being offered at Mission Bay Park.
 
Google Books
The Natives Are Friendly?
By J. K. Randle
Winchester, Hampshire: Hambleside Group
1986
Pg. 212:
However, the Chinese philosopher Chu Mien said it all:
 
“There are three things that cannot be recalled -
A spent arrow
A spoken (broken) word
A lost opportunity.”
 
Google Books
The Routledge Book of World Proverbs
By Jon R. Stone
New York, NY: Routledge
2006
Pg. 267:
Four things come not back: the spoken word, the spent arrow, the past life, and the neglected opportunity. (Chinese)
 
Google Books
Bridge:
A Thinker’s Game
By Joe Blatnick
Bloomington, IN: AuthorHouse
2013
Pg. 81:
This statement leads quite logically to the first four items that follow:
 
Four Things That Come Not Back:
The Spent Arrow
The Spoken Word
The Past Life
The Neglected Opportunity
 
Democrat & Chronicle (Rochester, NY)
Woman to watch: Kate Ulrich Saracene
By Michelle Inclema Shippers 6:01 p.m. EDT September 30, 2013
(...)
A person who has inspired me (and why): My mentor, Bill Roscoe, was the Director of Labor Relations at Xerox and my manager when I first graduated from college. He was the kindest, funniest, and most family-centered man I know, and had a very successful career at the same time. He taught me so much about how to be successful and how to prioritize and live life. He once advised me that there are three things in life you can never get back: (1) the spoken word, (2) the spent arrow, and (3) the missed opportunity. I often recall those words when I’m faced with an important decision. Those words, and Bill, made a real difference in my life.
   
Jamaica Observer
Cocktails With — Janice Allen
Sunday, May 25, 2014
(...)
What’s the best piece of advice you’ve ever received?
My mother recently reminded me of a memory verse she learned as a child…“There are four things that come not back: The spoken word, the spent arrow, the passed time, the neglected opportunity”. I believe if I can live by those words I will be good!