विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम्। श्रद्धाविरहितं यज्ञं तामसं परिचक्षते ॥

vidhi-hīnam asṛiṣhṭānnaṁ mantra-hīnam adakṣhiṇam śhraddhā-virahitaṁ yajñaṁ tāmasaṁ parichakṣhate

The sacrifice contrary to the ordinances, without distributing food, devoid of words of power and without gifts, empty of faith, is said to be of darkness.

In plain words: Worship is dark and empty when it ignores the proper rules, shares no food with others, leaves out the sacred words, gives no gifts to the priests, and has no faith behind it.