Chapter 17 · The Three Kinds of Faith · Krishna said
Bhagavad Gita 17.13 — Tamasic sacrifice
विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम्। श्रद्धाविरहितं यज्ञं तामसं परिचक्षते ॥
vidhihīnamasṛṣṭānnaṃ mantrahīnamadakṣiṇam | śraddhāvirahitaṃ yajñaṃ tāmasaṃ paricakṣate ||
Meaning
A sacrifice done without rules, without sharing food, without mantras, without gifts to the priests and without faith is called tamasic.