I remembered the same thing. Interestingly, there was a topic about this quote in this forum and the topic starter actually tattooed iterr, not really sure, but possibly 「端的只今の一念より外これなく候」?
Then see my reply #4. These lines appear in Book 11, Paragraph 1218. I put the corresponding Japanese text for each sentence, from "萬能一心" to "...七度虚言いふが男なり。".these are the teachings of Yamamoto Jin'emon:
Singlemindedness is all-powerful.
Tether even a roasted chicken.
Continue to spur a running horse.
A man who will criticize you openly carries no connivance.
A man exists for a generation, but his name lasts to the end of time.
Money is a thing that will be there when asked for. A good man is not so easily found.
Walk with a real man one hundred yards and he'll tell you at least seven lies.