What are the requirements for a witness to testify against an absent person?

Primary text

If the party being testified against is known by name, identity, and lineage, it is permissible to testify against them whether they are present or absent. If this comprehensive knowledge is lacking, one may not testify against them while they are absent. However, if they are present, testimony is permissible if the witness knows their specific identity (*ayn*). This was explicitly stated by Ahmad. If a witness testifies concerning a right one person has over another, but does not know the name of either party, it is permissible if both are present and state, 'I testify that this person has [a claim] against this person,' but if the party against whom the claim is made is absent, the witness may not testify until his name is known.