Muwatta Malik, Book 31, Hadith 1372 (In-Book)

Yahya related to me from Malik from Abu'z-Zinad from al Araj from Abu Hurayra that the Messenger of Allah, may Allah bless him and grant him peace, said, "Delay in payment by a rich man is injustice, but when one of you is referred for payment to a wealthy man, let him be referred."

حَدَّثَنَا يَحْيَى، عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ مَطْلُ الْغَنِيِّ ظُلْمٌ وَإِذَا أُتْبِعَ أَحَدُكُمْ عَلَى مَلِيءٍ فَلْيَتْبَعْ ‏" ‏ ‏.‏

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also referenced under: Book 31, Hadith 85 (USC-MSA)