فينعقد النكاح بشهادة الفساق
In this Hanafi usul argument, a marriage contract may be concluded in the presence of morally disqualified witnesses because the prohibition concerns acceptance of testimony, not the bare occurrence of the witnessing act.
Liʿān is treated differently: in this doctrinal argument it is not obligatory for a morally disqualified person, because liʿān consists of legally prescribed testimony-like declarations and disqualification affects their performance.
Together, the examples distinguish the occurrence, the admissibility, and the specific legal consequence of testimony. Recognition in one setting does not establish admission in every other setting.