Bg 17.13

vidhi-hinam asrstannam
mantra-hinam adaksinam
sraddha-virahitam yajnam
tamasam paricaksate

Word for word: 
vidhi-hinam — without scriptural direction; asrsta-annam — without distribution of prasadam; mantra-hinam — with no chanting of the Vedic hymns; adaksinam — with no remunerations to the priests; sraddha — faith; virahitam — without; yajnam — sacrifice; tamasam — in the mode of ignorance; paricaksate — is to be considered.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Any sacrifice performed without regard for the directions of scripture, without distribution of prasadam [spiritual food], without chanting of Vedic hymns and remunerations to the priests, and without faith is considered to be in the mode of ignorance.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Faith in the mode of darkness or ignorance is actually faithlessness. Sometimes people worship some demigod just to make money and then spend the money for recreation, ignoring the scriptural injunctions. Such ceremonial shows of religiosity are not accepted as genuine. They are all in the mode of darkness; they produce a demoniac mentality and do not benefit human society.