A samurai makes no second statement — i.e., someone of honor keeps their word and does not go back on what they said.
彼は約束したら必ず守る人だ。まさに武士に二言なしだ。
He's the kind of person who always keeps his promises. Truly, a man of his word.
上司が『この計画でいく』と言ったら、武士に二言なしで全員が従った。
When the boss said 'we'll go with this plan,' everyone followed without second thoughts.