وَجَزَاءُ سَيِّئَةٍ سَيِّئَةٌ مِثْلُهَا
The recompense for a wrong is a corresponding response of equal measure.
The first sayyiʾah denotes an actual wrong. The second repeats the word, but refers to a permitted corresponding recompense within its limits. It need not carry the first act's moral blame.
The central qualification is proportional response. Translating the second word without qualification as a fresh sin could distort the intended judgment. Mushākalah concerns the form of expression, not an assertion that wrong and lawful recompense have the same moral status.