Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 17

Sanskrit:

द्वौ मासौ तत्र चावात्सीन्मधुं माधवमेव च ।राम: क्षपासु भगवान् गोपीनां रतिमावहन् ॥ १७ ॥

ITRANS:

dvau māsau tatra cāvātsīnmadhuṁ mādhavaṁ eva carāmaḥ kṣapāsu bhagavāngopīnāṁ ratim āvahan

Translation:

Lord Balarāma, the Personality of Godhead, resided there for the two months of Madhu and Mādhava, and during the nights He gave His cowherd girlfriends conjugal pleasure.

Purport:

Śrīla Śrīdhara Svāmī states that the gopīs who enjoyed conjugal affairs with Śrī Balarāma during His visit to Gokula had not taken part in Śrī Kṛṣṇa’s rāsa dance, being too young at the time. Śrīla Jīva Gosvāmī confirms this statement by quoting a phrase from the Bhāgavatam (10.15.8) — gopyo ’ntareṇa bhujayoḥ — which indicates that there are particular gopīs who act as Lord Balarāma’s girlfriends. Furthermore, Jīva Gosvāmī states that during the Holī festivities celebrated when Kṛṣṇa killed Śaṅkhacūḍa, the gopīs Lord Balarāma enjoyed with were different from the ones Lord Kṛṣṇa enjoyed with. Śrīla Viśvanātha Cakravartī agrees with this explanation.