Agniveshyagrihyasutra 2.7.9.31

2.7.9.31

atha mahāyajñānām ekasminnahani mano jyotiḥ iti dvayostriṣu caturṣu pañcasu vā ṣaṭsu prabhṛtīti tisrastantumatīrhutvā catasro vāruṇīrjapet imaṃ me varuṇa tattvā yāmi yatkiñca ava te heḍa ityā navarātrāt \

Now, in the case of the great sacrifices: on one day with 'May Mind [and] Light…'; on two, three, four, or five; or beginning from six, having offered three Tantumatī verses, he should mutter the four Vāruṇī verses: 'This my [call], O Varuṇa…,' 'That I ask of thee…,' 'Whatever [sin]…,' and 'Loosen up thy wrath…,' up to nine nights.