To locate an omission, first identify the direction of the chain. Its beginning (mabda’) is the side nearest the compiler or later transmitter; moving toward the source leads through earlier narrators to the Companion and the Prophet ﷺ.
«فَالسَّقْطُ إِمَّا أَنْ يَكُونَ مِنْ مَبَادِئِ السَّنَدِ مِنْ تَصَرُّفِ مُصَنِّفٍ، أَوْ مِنْ آخِرِهِ أَيْ الْإِسْنَادِ بَعْدَ التَّابِعِي، أَوْ غَيْرِ ذَلِكَ»
The omission may occur at the chain's beginning by the compiler's presentation, at its end after a Successor, or elsewhere.
These locations distinguish mu‘allaq, mursal, and other interruptions. A second distinction asks whether the omission is obvious or concealed, leading to tadlis and hidden irsal.