Bhagavad Gita 17.13

17.13 They declare that sacrifice to be Tamasic which is contrary to the ordinances of the scriptures, in which no food is distributed, which is devoid of Mantras, gifts and faith.

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.