Deficient Ada (Ada Qasir) means that the act is performed, but a prescribed quality is missing.
Consider a late joiner, or Masbuq1. The part of prayer that this person completes alone lacks the congregation quality. That part is the example of deficient Ada.
“Deficient” identifies the missing quality; it does not, by itself, mean that no prayer was performed or that this prayer is invalid.
1. Masbuq: a worshipper who joined the congregation after missing an earlier part of the prayer.
- An Act Performed with a Missing Quality