17:13  

विधिहीनमसृष्टान्नं मन्त्रहीनमदक्षिणम् ।
श्रद्धाविरहितं यज्ञं तामसं परिचक्षते ॥१७- १३॥

widhihiinamasRRiShTaannaM mantrahiinamadakShiNam ।

shraddhaawirahitaM yadnyaM taamasaM parichakShate ॥१७- १३॥

Source: Automatic ITRANS Transliteration

Unmannered, failing to offer food, without mantras or tithe,
Devoid of devotion, sacrifice is despised as taamasic.

Source: Milind S. Pandit

Yajna that is performed without following the scripture, in which no food is distributed, which is devoid of mantra, faith, and gift, is said to be Taamasika Yajna.

Source: The Bhagavad-Gita: The Sacred Song

And that sacrifice performed in defiance of scriptural injunctions, in which no spiritual food is distributed, no hymns are chanted and no remunerations are made to the priests, and which is faithless--that sacrifice is of the nature of ignorance.

Source: Bhagavad Gita As It Is