TT #231 · 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 Sifrei Devarim 188.
TT lemma: בְּכׇל חֵטְא אֲשֶׁר יֶחֱטָא.
English: ‘In any sin that he may commit’ – to include all kinds of transgressions.
Derash universalizing the rule (Sifrei) — no category of sin is exempt from the two-witness requirement.
Whether the charge is capital, corporal, or monetary, a single witness is never sufficient to establish liability.