Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 31
Sanskrit:
ऊचु: पौरा अहो गोप्यस्तप: किमचरन्महत् ।या ह्येतावनुपश्यन्ति नरलोकमहोत्सवौ ॥ ३१ ॥
ITRANS:
ūcuḥ paurā aho gopyastapaḥ kim acaran mahatyā hy etāv anupaśyantinara-loka-mahotsavau
Translation:
The women of Mathurā exclaimed: Oh, what severe austerities the gopīs must have performed to be able to regularly see Kṛṣṇa and Balarāma, who are the greatest source of pleasure for all mankind!