SB 10.35.1

śrī-śuka uvāca
gopyaḥ kṛṣṇe vanaṁ yāte
 tam anudruta-cetasaḥ
kṛṣṇa-līlāḥ pragāyantyo
 ninyur duḥkhena vāsarān
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; gopyaḥ — the gopīs; kṛṣṇe — Lord Kṛṣṇa; vanam — to the forest; yāte — having gone; tam — after Him; anudruta — chasing; cetasaḥ — whose minds; kṛṣṇa-līlāḥ — the transcendental pastimes of Kṛṣṇa; pragāyantyaḥ — singing loudly; ninyuḥ — they passed; duḥkhena — unhappily; vāsarān — the days.
Śukadeva Gosvāmī said: Whenever Kṛṣṇa went to the forest, the minds of the gopīs would run after Him, and thus the young girls sadly spent their days singing of His pastimes.

Although the gopīs enjoyed direct association with Kṛṣṇa at night in the rāsa dance, during the day He went about His normal duties, tending His cows in the forest. At that time the minds of the gopīs would run after Him, but the young girls had to stay back in the village and do their own duties. Thus feeling the pain of separation, they would sing about Śrī Kṛṣṇa’s transcendental pastimes.