CC Ādi 1.72

rāsotsavaḥ sampravṛtto
gopī-maṇḍala-maṇḍitaḥ
yogeśvareṇa kṛṣṇena
tāsāṁ madhye dvayor dvayoḥ
Word for word: 
rāsa-utsavaḥ — the festival of the rāsa dance; sampravṛttaḥ — was begun; gopī-maṇḍala — by groups of gopīs; maṇḍitaḥ — decorated; yoga-īśvareṇa — by the master of all mystic powers; kṛṣṇena — by Lord Kṛṣṇa; tāsām — of them; madhye — in the middle; dvayoḥ dvayoḥ — of each two.
Translation: 
“When Lord Kṛṣṇa, surrounded by groups of cowherd girls, began the festivities of the rāsa dance, the Lord of all mystic powers placed Himself between each two girls.”
Purport: 

This verse is also quoted from Śrīmad-Bhāgavatam (10.33.3).