Khalid ibn Abi Bakr reported: Al-Hasan al-Basri, may Allah have mercy on him, said, “Cure your heart, for Allah Almighty requires the servants to have sound hearts.”
Source: al-Tawāḍu’ wal-Khumūl 240
عَنْ خَالِدِ بْنِ أَبِي بَكْرٍعَنِ الْحَسَنِ البصري رحمه الله قَالَ دَاوِ قَلْبَكَ فَإِنَّ حَاجَةَ اللَّهِ عَزَّ وَجَلَّ إِلَى الْعِبَادِ صَلَاحُ قُلُوبِهِمْ
240 التواضع والخمول لابن أبي الدنيا