I have combined these... just seems clearer.

"Of all said words, of tongue and pen, the saddest are these : what might have been." Silver Spoons 1x21 abt. 23:30.

"Of all sad words of tongue or pen, the saddest are these, 'It might have been.'"
or
"For of all sad words of tongue or pen, the saddest are these: 'It might have been.'"

? John Greenleaf Whittier