Musnad Ahmad 30:2848

Narrated to us Abd al-Rahman, from Sufyan, from Abu al-Zinad, from al-A’raj, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, that he said: "Delaying payment by the wealthy is injustice. And if one of you is referred to a solvent person, let him accept the referral."