What is the case of the oath of the testimony? [If] he says to two, “Come and testify for me,” [and they reply,] “We swear that we do not know any testimony for you”; or they say to him, “We do not know any testimony for you,” [and he says,] “I adjure you,” and they reply, “Amen!” —- they are liable.  [If] he adjured them five times outside of court, and they came to the court and confessed —- they are exempt. [If] they denied —- they are liable for each one. [If] he adjured them five times before the court, and they denied —- they are liable only once. Said R' Shimon: What is the reason? Because they cannot retract and confess.