One verse

Bhagavad Gita 17.13

17.13

विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम् | श्रद्धाविरहितं यज्ञं तामसं परिचक्षते ||१७-१३||

vidhihīnamasṛṣṭānnaṃ mantrahīnamadakṣiṇam . śraddhāvirahitaṃ yajñaṃ tāmasaṃ paricakṣate ||17-13||

vidhi-hīnam
without scriptural direction
asṛṣṭa-annam
without distribution of prasādam
mantra-hīnam
with no chanting of the Vedic hymns
adakṣiṇam
with no remunerations to the priests
śraddhā
faith
virahitam
without
yajñam
sacrifice
tāmasam
in the mode of ignorance
paricakṣate
is to be considered

Any sacrifice performed without regard for the directions of scripture, without distribution of prasādam [spiritual food], without chanting of Vedic hymns and remunerations to the priests, and without faith is considered to be in the mode of ignorance.