The principle of divine reward for those who do good (muhsinūn)

وَلَمَّا بَلَغَ أَشُدَّهُۥ وَٱسْتَوَىٰٓ ءَاتَيْنَـٰهُ حُكْمًا وَعِلْمًا ۚ وَكَذَٰلِكَ نَجْزِى ٱلْمُحْسِنِينَ

And when he attained his full strength and was [mentally] mature, We bestowed upon him judgement and knowledge. And thus do We reward the doers of good.