Surah Luqman 31:3

هُدًى وَرَحْمَةً لِّلْمُحْسِنِينَ

As guidance and mercy for the doers of good

Translation: Saheeh International

Tafsir

it is a guidance and a mercy read nominative rahmatun; the popular accusative reading rahmatan would make it a circumstantial qualifier referring to āyāt ‘signs’ the operator of which being the implicit demonstrative import of tilka ‘those’ for the virtuous

Excerpt from Tafsir al-Jalalayn, commentary on 31:3, via Quran.com. The reader has the full commentary and 9 more tafsirs.