«وَالْمُتَّصِلُ: مَا سَلِمَ إِسْنَادُهُ مِنْ سُقُوطٍ فِيهِ، بِحَيْثُ يَكُونُ كُلٌّ مِنْ رِجَالِهِ سَمِعَ ذَلِكَ الْمَرْوِيَّ مِنْ شَيْخِهِ»
A connected chain has no missing transmitter; each narrator received the relevant report from his teacher.
Writing the sequence “A from B from C” does not itself prove a historical transmission link. Researchers may need to examine chronology, whether meeting was possible or established, the mode of transmission, and other relevant evidence. The concern is whether this particular report passed through each purported link.
Example: If B could not have received the report from C and a middle transmitter has been omitted, the chain is disconnected even if its remaining narrators are exceptionally upright and accurate. The condition of ittisal is therefore unsatisfied.