أَثَبَتَتْ نِسْبَةُ الرِّسَالَةِ؟ قَالَ: بَعْدُ لَمْ تَثْبُتْ.
Has the letter's attribution been proved? He said: It has not yet been proved.
The antecedent of the disputed attribution is supplied by the question, so the answer can avoid repeating the full noun phrase. The wording remains short and intelligible through the immediate context. Merely noticing a short sentence does not automatically establish ījāz by ellipsis: identify the specific unexpressed material and its supporting clue.
If several unrelated attributions were simultaneously being discussed, the same omission might become ambiguous. Effective ellipsis depends upon recoverable reference, not a mechanical preference for fewer words.