Mishkat al-Masabih 11 Business Transactions كتاب البيوع 163

وَعَنْ عِمْرَانَ بْنِ حُصَيْنٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ كَانَ لَهُ عَلَى رَجُلٍ حَقٌّ فَمَنْ أَخَّرَهُ كَانَ لَهُ بِكُلِّ يَوْمٍ صَدَقَةٌ» . رَوَاهُ أَحْمد

‘Imran b. Husain reported God’s Messenger as saying, “When anyone has something due to him from another he will be credited with sadaqa for every day he allows the other to postpone payment.” Ahmad transmitted it.