Bhagavad Gita Chapter 17, Verse 13

विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम् | श्रद्धाविरहितं यज्ञं तामसं परिचक्षते ||

vidhi-hīnam asṛṣṭānnaṁ mantra-hīnam adakṣiṇam śraddhā-virahitaṁ yajñaṁ tāmasaṁ paricakṣate

Sacrifice that is performed without scriptural injunctions, without distribution of food, without mantras, without dakshina, and without faith—that is declared to be tamasic.

Krishna describes tamasic sacrifice—sacrifice that is tamasic. 'Vidhi-hīnam asṛṣṭānnaṁ mantra-hīnam adakṣiṇam śraddhā-virahitaṁ yajñaṁ'—this sacrifice is without scriptural injunctions (vidhi-hīnam), without distribution of food (asṛṣṭānnam), without mantras (mantra-hīnam), without dakshina (adakṣiṇam), and without faith (śraddhā-virahitam). 'Tāmasaṁ paricakṣate'—it is declared (paricakṣate) to be tamasic (tāmasam). Tamasic sacrifice is performed negligently, without proper form, without understanding, and without faith. It's not about duty or results—it's about going through the motions without care or understanding. Understanding this helps you recognize tamasic sacrifice and avoid it.