COMMENTARY on 4:23
A. Yusuf Ali:

Translation:
Prohibited to you (For marriage) are:- 531 Your mothers, daughters, 532 sisters; father´s sisters, Mother´s sisters; brother´s daughters, sister´s daughters; foster-mothers 533 (Who gave you suck), foster-sisters; your wives´ mothers; your stepdaughters under your 534 guardianship, born of your wives to whom you have gone in,- no prohibition if you have not gone in;- (Those who have been) wives of your sons 535 proceeding from your loins; and two sisters in wedlock at one and the same time, 536 except for what is past; for Allah is Oft-forgiving, Most Merciful;-
Commentary:

531  This Table of Prohibited Degrees agrees in the main with what is usually accepted among all nations, except in minor details. It begins in the last verse (with father's widows or divorcees). The scheme is drawn upon the assumption that the person who proposes to marry is a man; if it is a woman, the same scheme will apply, mutatis mutandis; it will read: "your fathers, sons, brothers," etc.; or you can always read it from the husband's view of relationship, as there must always be a husband in a marriage.

532  "Mother" includes grandmother (through the father or mother), great - grandmother, etc.; "daughter" includes granddaughter through son or daughter), great-granddaughter, etc.; "sister," includes full-sister and half-sister. "Father's sister" includes grandfather's sister, etc. and "mother's sister" includes grandmother's sister, etc.

533  "Fosterage" or milk-relationships play an important part in Muslim Law, and count like blood-relationships; it would therefore seem that not only fostermothers and foster-sisters, but foster-mother's sister, etc., all come within the prohibited degrees.

534  It is generally held that "under your guardianship" is a description, not a condition. (R).

535  "Sons" includes grandsons, but excludes adopted sons, or persons treated as such, on account of the words "proceeding from your loins" (Cf. 33:4).

536  The bar against two sisters in marriage together applies to aunt and niece together, but not to deceased wife's sister after the wife dies.

 

Muhammad Asad:

Translation:
Forbidden to you are your mothers, and your daughters, and your sisters, and your aunts paternal and maternal, and a brother's daughters, and a sister's daughters; and your milk-mothers, and your milk-sisters; and the mothers of your wives; and your step-daughters - who are your foster children - born of your wives with whom you have consummated your marriage; but if you have not consummated your marriage, you will incur no sin [by marrying their daughters]; and [forbidden to you are] the spouses of the sons who have sprung from your loins; and [you are forbidden] to have two sisters [as your wives] at one and the same time - but what is past is past: 25 for, behold, God is indeed much-forgiving, a dispenser of grace.
Commentary:
25  See preceding note.