What is the evidence for the validity of hawala (transfer of debt) in the Holy Quran, and is it permissible for the transferee to refuse to hand over the debt to the assignee?

The Hawala (transfer of debt) is established by the Sunnah and the consensus of Muslims. This is indicated by the Prophet's (peace be upon him) saying: "The delay in payment by a wealthy person is injustice, and whoever is referred to a rich person, let him follow him." As for the Quran, there is no explicit text on Hawala, but it falls under the general meaning of His (the Almighty's) saying: "And whatever the Messenger gives you, take it; and whatever he forbids you from, abstain." The transferee is not permitted to refuse to deliver the debt to the assignee, because the Hawala is a binding contract for him, unless he proves harm to himself or enmity that might drive him to exact the right in an inappropriate manner.