“[On writing:] "There's a great quote by Julius Irving that went, 'Being a professional is doing the things you love to do, on the days you don't feel like doing them.'"

(, interview with Budd Mishkin;, March 25, 2007.)”

Original: Fare ogni giorno ciò che vi piace vi farà sentire molto soddisfatti. E l'unico modo per fare bene ciò che vi piace sarà amare ciò che fate.
Source: prevale.net

The Quote Investigator http://quoteinvestigator.com/tag/virginia-woolf/ traces the origin of such statements to The Intimate Notebooks of George Jean Nathan (1932), where the diarist states:
We were sitting one morning two Summers ago, Ferenc Molnár, Dr. Rudolf Kommer and I, in the little garden of a coffee-house in the Austrian Tyrol. “Your writing?” we asked him. “How do you regard it?” Languidly he readjusted the inevitable monocle to his eye. “Like a whore,” he blandly ventured. “First, I did it for my own pleasure. Then I did it for the pleasure of my friends. And now — I do it for money.”
Misattributed

Letter (26 August 1940); published in Ernest Hemingway: Selected Letters 1917–1961 (1981) edited by Carlos Baker

Letter to Malcolm Cowley (14 November 1945); published in Ernest Hemingway: Selected Letters 1917–1961 (1981) edited by Carlos Baker

2010s, Farewell Speech (2017)
Context: !-- So the young people here and the young people out there: --> Do not ever let anyone make you feel like you don't matter, or like you don't have a place in our American story — because you do. And you have a right to be exactly who you are.
But I also want to be very clear: This right isn't just handed to you. No, this right has to be earned every single day. You cannot take your freedoms for granted. Just like generations who have come before you, you have to do your part to preserve and protect those freedoms. And that starts right now, when you're young.
Right now, you need to be preparing yourself to add your voice to our national conversation. You need to prepare yourself to be informed and engaged as a citizen, to serve and to lead, to stand up for our proud American values and to honor them in your daily lives. And that means getting the best education possible so you can think critically, so you can express yourself clearly, so you can get a good job and support yourself and your family, so you can be a positive force in your communities.

Variant: How do you spell love?
You don't spell it, you feel it.

Source: Talking with Kurt Loder on MTV's Famous Last Words show circa 1991.