Surah Az Zumar Tafseer

That is the reward of doers of good. So that Allah may expiate from them the evil of what they did and give them the reward, according to the best of what they used to do.

This is like the Ayah:

أُوْلَـيِكَ الَّذِينَ نَتَقَبَّلُ عَنْهُمْ أَحْسَنَ مَا عَمِلُواْ وَنَتَجَاوَزُ عَن سَيْيَـتِهِمْ فِى أَصْحَـبِ الْجَنَّةِ وَعْدَ الصِّدْقِ الَّذِى كَانُواْ يُوعَدُونَ

They are those from whom We shall accept the best of their deeds and overlook their evil deeds. (They shall be) among the dwellers of Paradise, a promise of truth, which they have been promised. (46:16)