Deuteronomy 19:15

עד אחד ONE WITNESS [SHALL NOT RISE UP AGAINST A MAN FOR ANY INIQUITY] — This is the classic passage from which the general principle is derived that wherever the term “witness” (עד) occurs in the Torah, it means two witnesses, unless it specifically mentions in connection with it the word אחד (Sanhedrin 30a). לכל עון ולכל חטאת [ONE WITNESS SHALL NOT RISE UP AGAINST A PERSON] FOR ANY INIQUITY OR ANY SIN — i.e. that his fellow man should be punished on account of his evidence either by bodily punishment or by a monetary punishment; but he may rise up against his fellow men to compel him to take an oath. If, for instance, one says to his fellow, “Return me the maneh which I lent you”, and he replies “I have nothing of yours in my possession”, and one witness testifies that he has, he (the defendant) must take an oath to satisfy him (Shevuot 40a; cf. Sifrei Devarim 188:9). על פי שני עדים [AT THE MOUTH OF TWO WITNESSES ... SHALL THE MATTER BE ESTABLISHED] — at their mouth, but not that they may write their evidence down in a letter and send it to the court, nor that an interpreter stand between the witnesses and the judges (Sifrei Devarim 188:10).

לֹֽא־יָקוּם֩ עֵ֨ד אֶחָ֜ד בְּאִ֗ישׁ לְכׇל־עָוֺן֙ וּלְכׇל־חַטָּ֔את בְּכׇל־חֵ֖טְא אֲשֶׁ֣ר יֶֽחֱטָ֑א עַל־פִּ֣י ׀ שְׁנֵ֣י עֵדִ֗ים א֛וֹ עַל־פִּ֥י שְׁלֹשָֽׁה־עֵדִ֖ים יָק֥וּם דָּבָֽר׃

One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he may commit: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established.