Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 26
Sanskrit:
उवास तस्यां कतिचिन्मिथिलायां समा विभु: ।मानित: प्रीतियुक्तेन जनकेन महात्मना ।ततोऽशिक्षद् गदां काले धार्तराष्ट्र: सुयोधन: ॥ २६ ॥
ITRANS:
uvāsa tasyāṁ katicinmithilāyāṁ samā vibhuḥmānitaḥ prīti-yuktenajanakena mahātmanātato ’śikṣad gadāṁ kāledhārtarāṣṭraḥ suyodhanaḥ
Translation:
The almighty Lord Balarāma stayed in Mithilā for several years, honored by His affectionate devotee Janaka Mahārāja. During that time Dhṛtarāṣṭra’s son Duryodhana learned from Balarāma the art of fighting with a club.