Amāvasyā-Pitṛtarpaṇa: Purūravas and the Soma-Based Ancestral Offering (अमावस्या-पितृतर्पण / सोमतर्पण-विधि)
तथा श्राद्धेषु दत्तान्नं मन्त्रः प्रापयते पितॄन् / एवं ह्यविफलं श्राद्धं श्रद्धादत्तं तु मन्त्रतः
tathā śrāddheṣu dattānnaṃ mantraḥ prāpayate pitṝn / evaṃ hyaviphalaṃ śrāddhaṃ śraddhādattaṃ tu mantrataḥ
So too, the food offered in śrāddha is conveyed by mantra to the Pitṛs. Thus śrāddha given with faith, and through mantra, is never fruitless.