Bhagavad Gita 17.13

विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम्।श्रद्धाविरहितं यज्ञं तामसं परिचक्षते॥

vidhihīnamasṛṣṭānnaṃ mantrahīnamadakṣiṇam |śraddhāvirahitaṃ yajñaṃ tāmasaṃ paricakṣate ||

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

Sacrifice that is contrary to scriptural command, that is unaccompanied by prayers or gifts of food or money, and is without faith—that is the product of ignorance.

Our plain-language meaning of this verse is waiting for scholar review.