Hadithcore
Mishkat al-Masabih, 2927

'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.

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

References1 variant
In-Book Reference
Book 11, Hadith 163