Is it permissible for a secondary witness (shahid far' / witness of the branch) to testify concerning one of the primary witnesses (shahid asl / witness of the origin)?
General Chapter
Al-Mughni
Book of Testimonies
Primary text
It is permissible for a branch witness to testify regarding one of the origin witnesses, meaning two branch witnesses testify concerning two origin witnesses. This view is held by Al-Qadi (Ibn Qudamah, referencing Ahmad), Shurayh, Al-Sha'bi, Al-Hasan, Ibn Shubrumah, Ibn Abi Layla, Al-Thawri, Ishaq, Al-Batti, Al-'Anbari, and Numayr ibn Aws. The evidence supporting this is that the matter is established by two witnesses, and two have testified to what establishes it, just as if they testified to the right itself. Furthermore, the branch witnesses are a substitute for the origin witnesses, so the number required for them should be the same as for the origin testimony. Ahmad and Ishaq state that the people of knowledge have continuously followed this practice. Finally, the branch witnesses do not transfer a right upon themselves from the origin witnesses, so their testimony should be accepted by a single person, similar to religious reports (akhbar al-diyanaat) where they only transmit testimony, not a right upon themselves.
Supporting text
The opposing view, held by Abu Hanifa, Malik, and Al-Shafi'i, maintains that it is not permissible for a branch witness to testify concerning an origin witness. Their reasoning is that the branch witnesses establish the testimony of the origin witnesses, and thus the testimony of each origin witness requires no less than two branch witnesses, analogous to how the confession of two confessors is not established by the testimony of only one witness for each confessor.