[Buying a Cheque for Less Than Its Face Value]

Answer—and Allah is the granter of success: What appears to me is that it is permissible. This is not from the category of sale and purchase; rather, it is from the category of “Reduce and take early (ḍaʿū wa taʿajjālū),” which is reported in the hadith and whose validity and permissibility scholars of the madhhab have affirmed.
The one who “bought” the cheque has, in effect, taken over the deferred debt guaranteed by the cheque and has advanced to the creditor his due in exchange for a known deduction; this is permissible and not a form of usury.
If it is said: A cheque is an instrument that, in banks, carries the ruling of paper currency; selling it for less than its face value is prohibited—either as usury or as currency exchange (ṣarf), for which equality is a condition.
We say: What we have mentioned is more fitting, for the cheque is nothing but a written remittance from a person to a bank. Moreover, what is incumbent—just as the scholars of the madhhab have stated—is that if a transaction admits of a construction that validates it and a construction that invalidates it, it should be carried upon the valid construction; and they have said that Muslims’ transactions must be presumed sound whenever possible.
As for wire transfers, the apparent ruling is permissibility as well. Although they may admit of invalid constructions, they also admit of a valid one—namely, to regard the discount as a form of hire (ijarah). It is as though one says: “Carry these funds for me to such-and-such a place, and your fee from them is such-and-such.”
If it is said: The remitter bears no burden in “carrying” them, because he has funds already on deposit in the countries to which he remits—so it is as if he is taking what he takes without counter-value.
We say: Even if the remitter does not physically travel with the funds, the remitter incurs costs in entries, bookkeeping, and accounting. He thus takes what he takes in exchange for that, while the owner of the funds pays what he pays in exchange for safeguarding his money from the dangers of the road—bandits, thieves—and the anxiety over it. Here there is giving and taking on both sides.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2