Is the specific verbal formulation 'Ashhadu' (I testify) required for rendering a legal testimony?

Primary text

The explicit verb form derived from the masdar (verbal noun) 'Shahadah' (testimony), namely 'Ashhadu' (I testify), is obligatory in rendering testimony. Alternative phrases such as 'A'lamu' (I know), 'Ahaqqu' (It is true), 'Atayaqanu' (I am certain), or 'A'rifu' (I recognize) are not accepted as valid testimony. This requirement is based on the necessity of using the specific verb form derived from the source noun of testimony, and because 'Shahadah' carries a specific legal meaning not present in other words, evidenced by its use in oaths, such as saying 'Ashhadu billahi' (I swear by God), and in mutual cursing (Li'an), which these other terms cannot substitute. This is the established position of Al-Shafi'i, with no known contrary opinion regarding the necessity of the term itself.