Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 21
Sanskrit:
ता वज्रकल्पा ह्यभवन् परिघा मुष्टिना भृता: ।जघ्नुर्द्विषस्तै: कृष्णेन वार्यमाणास्तु तं च ते ॥ २१ ॥
ITRANS:
tā vajra-kalpā hy abhavanparighā muṣṭinā bhṛtāḥjaghnur dviṣas taiḥ kṛṣṇenavāryamāṇās tu taṁ ca te
Translation:
As soon as they took these cane stalks in their fists, the stalks changed into iron rods as hard as thunderbolts. With these weapons the warriors began attacking one another again and again, and when Lord Kṛṣṇa tried to stop them they attacked Him as well.