In a report involving al-A‘mash, Abū ‘Awānah al-Waḍḍāḥ asked whether the particular report had been heard directly from Ibrāhīm al-Taymī. The reply disclosed an intermediary who had not appeared in the initial attribution.
«قُلْتُ لِلْأَعْمَشِ: سَمِعْتَ هَذَا مِنْ إِبْرَاهِيمَ؟ قَالَ: لَا، حَدَّثَنِي بِهِ حَكِيمُ بْنُ جُبَيْرٍ عَنْهُ»
I asked al-A‘mash: Did you hear this from Ibrāhīm? He replied: No; Ḥakīm ibn Jubayr narrated it to me from him.
Tadlis was established not merely from the word “ʿan,” but from investigation of hearing for this particular report and disclosure of the intermediate source. General contact with a teacher is distinct from receipt of a specific narration.