Bhagavad Gita Chapter 17 Verse 13

Gita 17.13

विधिहीनम्, असृृष्टान्नम्, मन्त्रहीनम्, अदक्षिणम्,
श्रद्धाविरहितम्, यज्ञम्, तामसम्, परिचक्षते।।13।।

Gita 17.13

Vidhiheenm’, asrshtaannm’, mantrheenm’, adakshinm’,
Shraddhaavirhitam’, yagyam’, taamsam’, parichakshte ||13||

Translation: (Vidhiheenm’) contrary to the scriptural injunctions (asrshtaannm’) without distribution of food (mantrheenm’) without actual mantras (adakshinm’) without giving gifts, without obtaining initiation and (shraddhavirhitam’) performed without faith (yagyam’) yagya i.e. religious rite (taamsam’) Tamas yagya (parichakshte) is said to be. (13)

Translation: A yagya i.e. religious rite which is contrary to the scriptural injunctions, in which no food is distributed, which is performed without actual mantras, without giving gifts, without obtaining initiation and without faith is said to be Tamas yagya.