That He prohibited the judge to declare punishments, or to make one liable for money, with the testimony of one witness - even if he was most fit. And that is His saying, "One witness may not arise against a man about any sin" (Deuteronomy 19:15). And they said (Shevuot 40a), "He may not arise 'about any sin,' but he may arise [to obligate someone in taking] an oath." And the regulations of this commandment have been explained in Chapter 9 of Sanhedrin. (See Parashat Shoftim; Mishneh Torah, Testimony 5.)