Bhagavad Gita
1.3

पश्यैतां पाण्डुपुत्राणामाचार्य महतीं चमूम् | व्यूढां द्रुपदपुत्रेण तव शिष्येण धीमता ||३||

paśhyaitāṁ pāṇḍu-putrāṇām āchārya mahatīṁ chamūm vyūḍhāṁ drupada-putreṇa tava śhiṣhyeṇa dhīmatā

Translation

Duryodhana said: O Teacher, behold this great army of the sons of Pandu, so expertly arranged by your intelligent disciple, the son of Drupada.

Interpretation

Duryodhana subtly points out that Dhrishtadyumna, who commands the Pandava forces, is Drona's own disciple — and one born specifically to kill Drona. This is a psychological challenge, testing Drona's loyalties and perhaps stirring guilt.