Is it a condition for the husband seeking li'an to have witnessed the adultery, or is complete certainty and evidence sufficient?

Protecting people's honor and preserving their dignity are among the objectives of Islam. Therefore, scholars have stipulated that if li'an (oath of condemnation) is due to an accusation of adultery, the husband must base his accusation on certainty, not on conjecture or doubt. It is stated in Al-Sharh Al-Kabir by Al-Dardir that for li'an due to an accusation of adultery, there must be visual certainty of the act of adultery, in a state that permits no other interpretation, or for a blind person, certainty through touch, or information that confirms it. Li'an is not sufficient based on evidence or indications that are not supported by the visual testimony of the husband or four witnesses.