«بِحَيْثُ لَا تَخْتَلِفُ الدَّلَالَةُ وَلَا يَخْتَلُّ الْبَيَانُ»
So that the indication of meaning is unchanged and the explanatory clarity is not impaired.
A shortened expression may remain grammatically complete yet mislead the listener. Dalālah concerns what the words assert or establish; bayān includes the clarification needed to identify the intended scope. Both must remain secure.
For illustration, take a non-hadith statement: “This person is entitled to the payment **if evidence is provided**.” Reproducing only “This person is entitled to the payment” erases a governing condition. The invented statement tests the principle; it is not attributed to the Prophet or to the source text.