Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 13
Sanskrit:
क्वचिन्नृत्यत्सु चान्येषु गायकौ वादकौ स्वयम् ।शशंसतुर्महाराज साधु साध्विति वादिनौ ॥ १३ ॥
ITRANS:
kvacin nṛtyatsu cānyeṣugāyakau vādakau svayamśaśaṁsatur mahā-rājasādhu sādhv iti vādinau
Translation:
While the other boys were dancing, O King, Kṛṣṇa and Balarāma would sometimes accompany them with song and instrumental music, and sometimes the two Lords would praise the boys, saying, “Very good! Very good!”