Bukhari

Hadith Commentary:
The objective of the chapter is also established from this hadith.
Because Ma'qil did not allow his sister to remarry Abu al-Badaah, even though the sister desired it, it is understood that marriage is under the authority of the guardian (wali).
According to reason as well, a woman should not be left completely independent; therefore, due to many benefits in matters of marriage, the presence of a guardian (wali) has been made obligatory.
The opinion of those who do not consider the presence of a guardian (wali) as a condition is incorrect.

Hadith Commentary:
(1)
The complete verse is as follows:
“And when you divorce women and they have fulfilled their waiting period (‘iddah), do not prevent them from marrying their [former] husbands if they agree among themselves in a lawful manner.” In this noble verse, although the act of marriage is attributed to the women, this does not abolish the guardian’s (wali’s) right of guardianship (wilayah); rather, while acknowledging his right, it is commanded that you should not be an obstacle in their marriage. If they have no authority, then what right do they have to be an obstacle? Reason also demands that a woman should not be left completely free, therefore, in view of the many benefits in matters of marriage, the permission of the guardian (wali) has been made obligatory. The position of those who do not accept the presence of a guardian as a condition is extremely questionable.

(2)
In reality, the intention of Imam Bukhari rahimahullah is that moderation and justice be established. However, our noble jurists (mujtahideen) on one hand have given adult women absolute freedom, that whenever and with whomever they wish, they may contract marriage, and that they have no need for a guardian. On the other hand, there is this utter chaos that if someone deceitfully makes a woman utter the words of proposal and acceptance (ijab wa qubul), which she understands, then she too will be bound in the contract of marriage and will have no right to free herself from it. But Imam Bukhari rahimahullah has chosen the path of moderation between these two extremes and has established this moderation from the ahadith. In fact, Imam Bukhari rahimahullah, in deriving rulings, keeps a deep eye on the welfare of people, and at the same time, he never lets go of the texts (nusus). Accordingly, Imam Bukhari rahimahullah, further on, establishes another chapter with these words:
(Bab: la yankihu al-ab wa ghayruhu al-bikr wa al-thayyib illa biridahuma)
“Neither the father nor anyone else may contract the marriage of a virgin (bikr) or a previously married woman (thayyib) except with their consent.”
The purpose of both these chapters is that neither is a woman absolutely free to marry whenever and wherever she wishes, nor is she so compelled and overpowered that her guardian may marry her off to whomever he wishes whenever he wishes, and she is forced to remain silent. Rather, to clarify this, he has established another chapter with these words:
(Bab idha zawwaja al-rajul ibnatahu wa hiya karihah fa nikahuhu mardud)
“When a father marries off his daughter by force while she dislikes it, then such a marriage is rejected.”