“Pooh, promise you won’t forget about me, ever. Not even when I’m a hundred.”
Pooh thought for a little.
“How old shall I  be then?”
“Ninety-nine.”
Pooh nodded.
“I promise,” he said.

A. A. Milne (1882-1956) English poet and playwright [Alan Alexander Milne]

The House at Pooh Corner, ch. 10 [Christopher Robin and Pooh] (1928)
    (Source)

Possibly the inspiration of the spurious Pooh quotation:

If you live to be a hundred, I want to live to be a hundred minus one day, so I never have to live without you.

For more discussion about this and related quotes, see May You All Live Forever. May I Live Forever Less A Day – Quote Investigator®.