I don't know which source i'm going to follow.
Some say its 3 molecules NADH per cycle → 2 cycles × (3 NADH) = 6 NADH
Some say its 4 molecules NADH per cycle instead?
This is slightly depending on which reaction you want to include into the cycle. I count four:
One when Pyruvate is converted to Acetyl-CoA,
one when Isocitrate is converted to α-Ketoglutarate,
one for the reaction of α-Ketoglutarate to Succinyl-CoA and
finally one for the reaction of Malate to Oxaloacetate.
If you see the reaction of Pyruvate as happening outside of the cycle, it's only the later three. See this image (from here) for an overview: