CC Ādi 5.136

vṛṣa hañā kṛṣṇa-sane māthā-māthi raṇa
kabhu kṛṣṇa kare tāṅra pāda-saṁvāhana
Word for word: 
vṛṣa hañā — becoming a bull; kṛṣṇa-sane — with Kṛṣṇa; māthā-māthi raṇa — fighting head to head; kabhu — sometimes; kṛṣṇa — Kṛṣṇa; kare — does; tāṅra — His; pāda-saṁvāhana — massaging the feet.
Translation: 
Playing like a bull, Lord Balarāma fights with Kṛṣṇa head to head. And sometimes Lord Kṛṣṇa massages the feet of Lord Balarāma.