Amar'e Stoudemire -- I'M FASTING FOR YOM KIPPUR ... Even Though I'm In Training Camp

Jewish NY Knicks star Amar'e Stoudemire says he'll be fasting for Yom Kippur when the sun goes down tonight ... and won't eat all day tomorrow ... despite the fact he's in the middle of NBA training camp.

Stoudemire just went to Instagram and posted ... "Day of Atonement !! Sundown tonight - Sundown tomorrow."

He added, "This is going to be the hardest one yet. No eating or drinking during camp."

It's kind of a big deal, considering the Knicks have been busting their asses during the training sessions ... and Stoudemire has vowed to refrain from nourishing himself after the brutal workouts.

FYI -- Amar'e's decision comes almost 49 years ... to the day ... from when Sandy Koufax famously decided to NOT pitch in a World Series game to observe the Jewish Holiday.