Amāvasyā-Pitṛtarpaṇa: Purūravas and the Soma-Based Ancestral Offering (अमावस्या-पितृतर्पण / सोमतर्पण-विधि)
यस्मात्तामनुमन्यन्ते पितरो दैवतैः सह / तस्मादनुमतिर्नाम पूर्णिमा प्रथमा स्मृता
yasmāttāmanumanyante pitaro daivataiḥ saha / tasmādanumatirnāma pūrṇimā prathamā smṛtā
Because the Pitṛs, together with the deities, give their assent to that tithi, it is called Anumatī; among the Pūrṇimās it is remembered as the first.