Bhagavad Gita: Chapter 1, Verse 14

ततः श्वेतैर्हयैर्युक्ते महति स्यन्दने स्थितौ ।
माधवः पाण्डवश्चैव दिव्यौ शङ्खौ प्रदध्मतुः ॥ १-१४॥

tataḥ śvetair hayair yukte mahati syandane sthitau
mādhavaḥ pāṇḍavaś caiva divyau śaṅkhau pradaghmatuḥ 1.14

On the other side, both Lord Krishna and Arjuna, stationed on a great chariot drawn by white horses, sounded their divine conch shells.