Barack Obama: "Unlike some people *cough*Michelle Obama*cough*...

... I write my own books."

Not a direct quote.

The writing has been going more slowly than he’d expected, and according to several people who have spoken with him, the 44th president is feeling competitive with his wife, whose own book, Becoming, was the biggest release of 2018 and is on track to be the best-selling memoir in history. Speaking on the condition of anonymity, like others in this story, these sources note he’ll occasionally say in conversation that he’s writing this book himself, while Michelle used a ghostwriter.

https://www.theatlantic.com/politics...ection/590056/

Now, this is all anonymous hearsay, and the Atlantic is not your friend. So while this may be an amusing (or annoying) bit of gossip, I'd recommend taking it with a grain of salt.