What is required of a witness for their testimony to be accepted?

Primary text

It is required that a witness be considered trustworthy in their word so that a strong presumption of their truthfulness is obtained. For this reason, justice ('adalah) is a prerequisite. One who frequently errs or is often inattentive is not relied upon, due to the possibility that their testimony stems from an error, such as testifying against the wrong person or for the wrong person, or regarding something other than what they were asked about. If one is inattentive, an opponent might mislead them regarding matters not related to the testimony, thus preventing trustworthiness. A rare error or rare inattention does not prevent testimony because no one is free from that; if it prevented testimony, the door to testimony would close. Therefore, frequency of error is considered a bar, just as the frequency of sins is considered a bar to justice.