Rigvidhana 2.3.16

2.3.16

kṛṣṇa pakṣe caturdaśyām tri rātra upoṣitaḥ śuciḥ./
dakṣiṇa pravaṇe deśe śmaśānasthaḥ samāhitaḥ.//

Fasting for three nights on the fourteenth day of the dark fortnight, pure, / standing in a cremation ground in a region sloping to the south, concentrated,