Tafsir of An-Nisa' 4:20

(And if you desire) O husbands, (to replace one wife) i.e., to establish one woman whom you desire (in place of a wife) i.e., a woman whom you desire to forsake by divorcing her, (and you have given) i.e., one of you has given (to one of them) i.e., to one of the wives, for the intent of "wife" is the genus that applies to multiple individuals, which is appropriate for the plural address. The intent of "giving," as Al-Karkhi said, is commitment and guarantee, as in the saying of the Exalted: "provided you give them their due dowries," meaning what you have committed to and guaranteed. The concept of the condition is not intended, according to what some researchers have stated; rather, it is mentioned because, in that situation, one might mistakenly think that taking is permissible, so they were alerted to the ruling regarding it. The sentence is in the state of a circumstantial clause with the assumption of "qad" (already), not coordinated with the condition; meaning: "While you have already given to the one whom you desire to divorce and replace with another (a qintar) i.e., much wealth—and the various opinions regarding it have preceded—(then do not take from it) i.e., from the qintar that was given (anything) (Page V04P243) even a small amount, let alone a large amount.

(Would you take it) i.e., the thing, (by way of slander and manifest sin?) This is a new beginning intended to confirm the prohibition, and the interrogation is for the purpose of denial and rebuke. Both nouns [slander and sin] are in the accusative case as circumstantial qualifiers, interpreted as descriptions; meaning, "Would you take it while being slanderers and sinners?" It is also possible that they are in the accusative as causes, and there is no difference in this regard between a final cause and a motivating cause. What we are dealing with is the latter, such as the saying: "I refrained from war out of cowardice," because the taking is due to their slander and their commission of sins. It has been said: A man among them, when he desired a new [wife], would slander the one beneath him with an indecency so that he might force her to relinquish what he had given her in order to spend it on marrying the new one. Thus, they were forbidden from that. Buhtan (slander) is the lie that causes the one lied about to be confounded. Al-Zajjaj said: It is the falsehood that causes one to be perplexed by its invalidity. It is interpreted here as injustice. It is narrated from Mujahid that it is "sin," and "sin" was coordinated with it for the purpose of explanation, as in the saying:

And he found her speech to be a lie and a fabrication.

It is also said: The intent of it here is the denial of ownership, and "manifest" means clear and apparent.