«أَنْ يَرْوِيَ جَمَاعَةٌ الْحَدِيثَ بِأَسَانِيدَ مُخْتَلِفَةٍ»
Several transmitters narrate a hadith through different chains.
If a later narrator presents their material under one undifferentiated chain, concealing which route carried which wording, listeners may believe every part was transmitted identically by all the authorities. This is a form of mudraj al-isnād.
Illustration: Teacher A transmits one version through Zayd's chain, and teacher B another through ʿAmr's chain. A pupil fuses the two and attributes the whole combined text to both routes. Scholarship must recover the distinct chains and any genuinely shared wording. Collecting chains is not itself defective; the problem is misrepresenting their differences.