Under Deuteronomy 19:15, how many witnesses were needed to establish a matter?

Answer: Two or three

A lone witness was not enough; a matter had to be established by the testimony of two or three witnesses.

“A lone witness is not sufficient to establish any wrongdoing or sin against a man, regardless of what offense he may have committed. A matter must be established by the testimony of two or three witnesses.”— Deuteronomy 19:15 (BSB)