Musannaf Ibn Abi Shaybah

Ibrahim says that in every transaction, revocation is permissible; however, if a person says to another, "I sell to you that item which is with so-and-so and so-and-so, and I sell it for such and such amount," if he completes the sale, then revocation is not permissible.

Hazrat Hakam bin Utaybah says that in the case of transfer of debt (hawalah), one cannot refer back to the original debtor unless he becomes insolvent or dies and leaves no means to fulfill the agreement, because a person is sometimes wealthy and sometimes insolvent.

Hazrat Uthman (may Allah be pleased with him) says regarding Hawalah that it can be revoked; the wealth of a Muslim will not be allowed to go to waste.

Hasan says that when a person gave something in a state of wealth and later became poor, then that wealth is permissible for him.

Hazrat Khattab Asfari says that a man referred me to some goods deposited with a Jew, and that Jew refused to give me the goods and kept making excuses. So I asked Hazrat Sha'bi about this matter, and he said: "Refer to the previous (agreement)."

Hazrat Shurayh says that if a person deposits his wealth with another, and the latter destroys that wealth, then the matter will be referred back to the first person.

It is narrated similarly through another chain of transmission.

Hazrat Sha'bi considered it undesirable for a person to say, "I buy this thing from you in exchange for that thing which is with so-and-so." Hazrat Sha'bi says that this is gharar (a transaction involving something not present).

They did not consider a good reference as acquittal; however, when the rightful owner truly acquits, then acquittal will occur.