Unfamiliar terms

1. warq: silver, whether minted into coin or left unminted.
2. “wa-lā tushaffū baʿḍahā ʿalā baʿḍ” — the first letter is read with ḍamma, the shīn with kasra, and the fā is doubled. It means, “Do not give some of it preference over the rest,” i.e., do not allow one amount to exceed the other. The verb is quadriliteral, taken from ashafa and shaff (increase), yet it can also be used for decrease, making it a word that carries opposite meanings.

Overall meaning
In this noble ḥadith the Prophet ﷺ forbids both kinds of ribā: that of excess (faḍl) and that of deferment (nasīʾa).
He prohibits selling gold for gold—whether the two amounts are coined or uncoined—unless they are exactly equal, weight for weight, and both parties take possession in the very session of contract; one may not be delivered while the other is deferred.
Likewise, he forbids selling silver for silver, coined or uncoined, unless the two amounts match, weight for weight, and mutual possession is completed in the contract session.
Thus no party may take more than the other, and they may not separate before mutual delivery.

Points derived from the ḥadith

1. It is forbidden to sell gold for gold or silver for silver—minted, unminted, or mixed—unless the quantities are identical according to the Islamic standard, namely weight, and unless both parties complete delivery in the contract session.
2. This prohibition renders the transaction unlawful and the contract invalid.
3. Equality of amount and hand-to-hand delivery within the contract session are conditions for every commodity susceptible to ribā; the criteria that unite such commodities will be set out, God willing.
4. Shaykh al-Islām Ibn Taymiyya said about a man who lends people one hundred and stipulates repayment of one hundred forty, calling it a “loan on silk”: “This is the very ribā about which the Quran was revealed.” He clarified that the lender deserves only what he originally gave or its exact equivalent; he has no right to any surplus. Whatever extra he has already collected by relying on a (mistaken) juristic interpretation is forgiven, but whatever remains outstanding in people’s debts is cancelled, in keeping with the Almighty’s words: “and give up what remains of ribā” (Q 2:278).