Fuṣṣilat 41:45-46

"We gave Moses (Mūsā) the Book, and disagreement arose over it… Whoever does righteous work, it is for himself; whoever does evil, it is against himself. Your Lord is not one who wrongs His servants."

فَٱخْتُلِفَ فِيهِ — the verb is passive: who it was that fell into disagreement is not stated.

This is a line treated at several points in this corpus: al-Baqara 2/213 and 2/253, al-Jāthiya 45/17. All of them say the same thing: the disagreement arises after the Book has come. I rely on those treatments.

The function of the verse here is consolation: wa lawlā kalimatun sabaqat min Rabbika la-quḍiya baynahum — had a word not gone before, judgement would have been passed between them. That is, the delay is not indifference.

بِظَلَّٰمٍ لِّلْعَبِيدِ — ẓallām is an intensive form (faʿʿāl).

The lexicographers dwell on what the form does here, and two explanations are transmitted:

I transmit both explanations; I do not impose a preference. On either reading the ruling of the sentence comes out in the same place: the recompense is tied to the person's own deed — the preceding sentence had already said this in both directions.