Bhagavad Gita 17.13
विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम्। श्रद्धाविरहितं यज्ञं तामसं परिचक्षते।।17.13।।
vidhihīnamasṛṣṭānnaṃ mantrahīnamadakṣiṇam| śraddhāvirahitaṃ yajñaṃ tāmasaṃ paricakṣate||17.13||
vidhihinamasrishtannam mantrahinamadakshinam shraddhavirahitam yajnam tamasam paricakshate17.13
Meaning
Sacrifice performed without regard for scriptural injunctions, without distributing food, without mantras, without gifts to the priests, and without faith — that is tamasic sacrifice.
शास्त्रविधि से रहित, अन्नदान से रहित, बिना मन्त्रों, बिना दक्षिणा और बिना श्रद्धा के किये हुए यज्ञ को तामस यज्ञ कहते हैं।
This is verse 13 of 28 in Chapter 17 (Shraddhatraya Vibhaga Yoga) of the Bhagavad Gita.