Sayyiduna Abu Hurayra (radi Allahu anhu) reported from the Glorious Messenger (sallal laahu alaihi wasallam) who said: “The two (seller and buyer) must not part away except by mutual consent.” (Abu Da’ood)
Sale is contracted by a declaration and acceptance expressed unequivocally in words or in expressions conveying the same meaning. The acceptance may be deferred until the breaking up of the meeting whether the declaration be made personally or by letter or message. An offer made by the purchaser cannot be restricted by the seller or to any particular parts of the goods. A little deviation from the offer or acceptance will not make the sale complete. A sale may be entered into either for ready money or for payment within a fixed time. Gains may be sold for other gains of different species.
There are four kinds of sale: