TT #232 · Parashas Shoftim · Sixth Aliyah · Passuk 19:15
A single witness shall not rise up against a man for any iniquity or for any sin, in any sin that he may commit; by the mouth of two witnesses or by the mouth of three witnesses a matter shall be established.
Torah Temimah points to Sanhedrin 30a.
TT lemma: עֵד אֶחָד.
English: ‘A single witness’ – even if he is as trustworthy as Moshe Rabbeinu.
Derash rejecting exceptions based on character (Bavli) — even the most reliable individual is still only one witness.
No matter how trustworthy a single witness may be, the Torah still requires two or three for the matter to be established.