844 – Ibn ʿUmar (may Allah be pleased with them both) related that the Messenger of Allah (blessings and peace be upon him) said, “None of you may propose to a woman who is already the object of another Muslim’s proposal, unless the first suitor withdraws or grants him permission.” Agreed upon, and the wording is that of al-Bukhari. (1)

Vocabulary of the ḥadith
• lā yakhtub: the particle lā is prohibitive, placing the verb that follows in the jussive mood; the verb comes from the pattern faʿala (e.g., qatala).
• al-khitbah (with a kasrah on the khāʾ): seeking a woman’s hand in marriage (engagement).
• al-khatībah: the woman who has been proposed to.

Points derived from the ḥadith
1 – It is forbidden to present a marriage proposal to a woman who has already been engaged by another Muslim; the default legal force of a prohibition is that it entails impermissibility.
2 – Al-Kashshāf summarizes: it is not lawful for a man to propose to a woman over the engagement of a fellow Muslim if the second suitor is aware of the first one’s proposal. Should he nevertheless do so and a contract be concluded, the marriage remains valid because the prohibition does not pertain to the very essence of the contract; therefore it does not invalidate it (although a scholarly dispute on this point will be mentioned later).
3 – If the second suitor was unaware of the earlier proposal, he is excused and the engagement is permissible; likewise, if the first proposal is declined, or if the first suitor authorizes the second, or if the first suitor simply abandons the idea of marrying her, then the second may legitimately propose.
4 – Neither the guardian nor the woman herself is blameworthy for retracting a prior acceptance when there is a sound reason, because marriage is a contract that endures and may bring harm; she therefore has the right to safeguard her own interest. Retracting without a valid reason is disliked on the part of both the guardian and the woman because it involves breaking a promise, yet it is not unlawful, for no obligatory right has yet been established.