Exact Source/citation Sam Walton Quote

Everyone and his brother cites the following quote from Sam Walton,
founder of Wal-Mart:

"Outstanding leaders go out of the way to boost the self-esteem of
their personnel.  If people believe in themselves, it's amazing what
they can accomplish.  High expectations are the key to everything."

However, I can't find the origin anywhere. I need the exact
citation--Book, page number etc...or the magazine/newspaper if it was
an interview.

Thanks.

Outstanding leaders go out of the way to boost the self-esteem of
their personnel. If people believe in themselves, it's amazing what
they can accomplish.

--Sam Walton quoted in Leadership Wired v6i15

This source doesn't list a page number, but I thought it was better
than nothing and it gives you a place to start.