Bhagavatapurana 8.21.26

8.21.26

atha tārkṣyasuto jñātvā virāṭ prabhucikīrṣitam /
babandha vāruṇaiḥ pāśairbaliṃ sūtye 'hani kratau //

26. Then having understood what the Lord expected him to do, the son of Tarkshya, a brilliant bird, bound Bali with the ropes of Varuna on the _sutya_ day (the day for extracting the juice of soma) of the sacrifice.