Shevuos 4:11-12

Shevuos 4:11

Let’s say that a litigant says to two men, “I call upon you, Person X and Person Y, that if you know of information on my behalf, you come and testify” and they reply, “We swear that we do not know of any information on your behalf.” If they had such information but it was based on hearsay, or if one of them was related to one of the litigants or otherwise unqualified to testify, they are exempt.

Shevuos 4:12

If the litigant sent his servant to call upon the witnesses, or if the one being sued said to them, “I call upon you that if you have any information on the plaintiff’s behalf, that you come and testify for him” – in these cases, the witnesses are exempt until they are called upon directly by the plaintiff.