Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 75: The History of the Bows of Lord Śiva and Lord Viṣṇu
Text 1.75.26

न्यस्तशस्त्रे पितरि मे तपोबलसमन्विते।
अर्जुनो विदधे मृत्युं प्राकृतां बुद्धिमास्थितः॥

nyasta-śastre pitari me tapo-bala-samanvite
arjuno
vidadhe mṛtyuṁ prākṛtāṁ buddhim āsthitaḥ

nyasta-śastre = when renounced the weapon; pitari me = my father; tapaḥ-bala-samanvite = who was endowed with the strength of austerity; arjunaḥ = Kārtavīryārjuna; vidadhe mṛtyum = killed him; prākṛtām buddhim āsthitaḥ = due to his materialistic conception of life.

When my father who was endowed with the strength of austerity renounced the weapon, Kārtavīryārjuna killed him due to his materialistic conception of life.