Sufyan Ibn ‘Uyayna said,
كان العلماء فيما مضى يكتب بعضهم إلى بعض هؤلاء الكلمات : مَنْ عَمِلَ لِآخِرَتِهِ كَفَاهُ اللَّهُ دُنْيَاهُ ، وَمَنْ أَصْلَحَ مَا بَيْنَهُ وَبَيْنَ اللَّهِ كَفَاهُ اللَّهُ النَّاسَ ، وَمِنْ أَصْلَحَ سَرِيرَتَهُ أَصْلَحَ اللَّهُ عَلَانِيَتَهُ”
“The scholars of the past used to write to one another with the following words. ‘Whoever works for his Hereafter, Allah will take care of his dunya. Whoever corrects what is between himself and Allah, Allah will correct what is between him and people, and whoever corrects his internal affairs (purifies his heart) Allah will correct for him his public affairs.