Musnad Abu Ya'la al-Mawsili 159:96

Suwayd ibn Sa'id narrated to us, from Malik, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Delaying payment by a wealthy person is an injustice. And if one of you is referred to a solvent person [to collect a debt], let him accept the transfer."