Okla. Stat. tit. 21, § 21-564: Privilege of witnesses in respect to claims or debts sold

No person shall be excused from testifying in any civil action,

to any facts showing that an evidence of debt or thing in action has

been bought, sold or received contrary to law, upon the ground that

his testimony might tend to convict him of a crime. But no evidence

derived from the examination of such person shall be received

against him upon any criminal prosecution.