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SB 10.34.20

kadācid atha govindo
 rāmaś cādbhuta-vikramaḥ
vijahratur vane rātryāṁ
 madhya-gau vraja-yoṣitām
Synonyms: 
kadācit — on one occasion; atha — then; govindaḥ — Lord Kṛṣṇa; rāmaḥ — Lord Balarāma; ca — and; adbhuta — wonderful; vikramaḥ — whose deeds; vijahratuḥ — the two of Them played; vane — in the forest; rātryām — at night; madhya-gau — in the midst; vraja-yoṣitām — of the women of the cowherd community.
Translation: 
Once Lord Govinda and Lord Rāma, the performers of wonderful feats, were playing in the forest at night with the young girls of Vraja.
Purport: 

This verse introduces a new pastime. According to the ācāryas, the occasion mentioned here is the Holikā-pūrṇimā, a day also known as Gaura-pūrṇimā.