«وَإِنِ اشْتَرَكَ اثْنَانِ فِي شَيْخٍ، وَتَقَدَّمَ مَوْتُ أَحَدِهِمَا عَلَى الآخَرِ، فَهُوَ السَّابِقُ وَاللَّاحِقُ»
“When two transmitters share a teacher and one dies earlier than the other, this is al-sābiq wa-l-lāḥiq.”
The sābiq is the pupil who died earlier; the lāḥiq is the one who died later. The case is especially striking when a substantial interval separates their dates of death.
The category requires two elements: a shared teacher and differing pupil death dates. Merely finding two narrators who died in different periods is insufficient without establishing their common source.