Bhagavad Gita, Chapter 17, Verse 13

The Yajna performed without heed to ordinance, in which no food is distributed, which is devoid of Mantras, gifts, and Shraddhâ, is said to be Tâmasika.

Even the outward form of sacrifice is described here as hollow once faith and real substance are missing.

Krishna names exactly what's absent, faith, proper offering, real donation, rather than leaving the failure vague. What's missing defines this mode as clearly as what's present defines the others.