Amāvasyā-Pitṛtarpaṇa: Purūravas and the Soma-Based Ancestral Offering (अमावस्या-पितृतर्पण / सोमतर्पण-विधि)
अन्तःसारमयस्येन्दोः पक्षयोः शुक्लकृष्णयोः / ह्रासवृद्धी पिदृमतः पित्र्यस्य च विनिर्णयम्
antaḥsāramayasyendoḥ pakṣayoḥ śuklakṛṣṇayoḥ / hrāsavṛddhī pidṛmataḥ pitryasya ca vinirṇayam
It sets forth the waning and waxing of the Moon, whose nature is inner essence, in the bright and dark fortnights, and determines the doctrine of the Pitṛ-world and the pitrya rites.