Kommentar zu Shevuot 4:10

/אם יודעים לי עדות וכו' פטורין – as it is written (Leviticus 5:1): “although able to testify” util he specifies his witnesses.

[If] he stood in the synagogue and said, “I adjure you that if you know any testimony for me you should come and bear testimony for me”, they are exempt unless he directs himself to them. If the litigant stood in a public place and adjured a large, unspecified crowd of people that they should testify for him, and they all swore that they knew no testimony, the ones who did in fact know testimony are nevertheless exempt. The mishnah teaches that the litigant must specify exactly who he is adjuring. When learning this mishnah we must remember that people who witness an event have a religious duty to testify, regardless of whether the litigant adjures them or not. Our mishnah merely teaches that they have not sworn a false oath unless specifically adjured.