Moyes told reporters that West Ham had made one bid of 6 million pounds, but were informed there was no deal to be done.
"They did ask if there was a figure (that would be acceptable) and we said 'no'," he added.
"Myself, (chief executive) Martin Bain, and (owner) Ellis Short are in agreement -- categorically, Jermain Defoe is not for sale."
Relegation-threatened Sunderland desperately need Defoe's firepower, with the 34-year-old scoring 11 goals in 20 Premier League appearances this season.
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Sunderland have scored only 19 goals in total and are 18th, level on points with Swansea City in the drop zone and two clear of bottom club Hull City.
The former England international, who started his professional career at West Ham, scored both goals from the penalty spot in the 2-2 draw with Liverpool at the Stadium of Light on Monday.
Moyes said Defoe could feature in the FA Cup third round tie against Burnley on Saturday because of player absences due to the African Nations Cup.
"We have had a few additions but the three boys we have lost to the African Cup of Nations this week sort of makes that smaller, but nevertheless it’s the same group of players so we won’t be far off the same boys we play most weeks," he said.
"We will need Jermain to be around it because we just don’t have enough people around to say we’re resting you this week."
(Reporting by Alan Baldwin, editing by Toby Davis)
