Bukhari

Hadith Commentary:
Within the bounds of the Shari’ah, it is permissible to have up to four wives at the same time, provided that justice can be maintained among them; otherwise, only one wife is required.
Some have translated it as: “In this Ummah, the best people are those who have many wives.”
The meaning is within the bounds of the Shari’ah: if a man is in need and can please all (his wives) with justice and fulfill their rights, then only four wives are permitted. To have more than four wives at the same time in marriage is absolutely forbidden (haram) in Islam.
Rather, the Noble Qur’an has clearly declared:
﴿فَإِنْ خِفْتُمْ أَلَّا تَعْدِلُوا فَوَاحِدَةً﴾
“If you fear that you will not be able to do justice, then (marry) only one.”
In this case, never keep more than one.
The Messenger of Allah (sallallahu alayhi wa sallam) in the last part of his life had nine wives in his household at the same time; this was among his (sallallahu alayhi wa sallam) unique characteristics. If anyone thinks that his intention was lust or indulgence, then such an assumption is absolutely incorrect, because in the prime of his youth, he (sallallahu alayhi wa sallam) was content with an elderly woman, Khadijah (radi Allahu anha). In keeping nine wives at the end of his life, there were many religious and worldly benefits, the details of which those interested may consult at this point in the commentary of Wahidi.
Among the number nine, there were several elderly widowed women whom he (sallallahu alayhi wa sallam) accepted into marriage purely for communal benefit.

Hadith Commentary:
(1)
Within the bounds of Shariah, a person is permitted to have up to four wives at the same time, provided that he deals justly among them and possesses the ability to fulfill their rights. However, it is forbidden (haram) to have more than four wives at the same time.

(2)
The Messenger of Allah (sallallahu alayhi wa sallam) had nine wives towards the end of his life. The purpose of having so many wives was not, Allah forbid, due to lust or indulgence, but rather for religious and many worldly benefits. Among them were several elderly widows whom he (sallallahu alayhi wa sallam) accepted in marriage solely for communal and national interests.

(3)
Despite this, some Westernized, liberal-minded women have objected, asking: "What kind of justice is this, that a man may marry four women, but a woman must suffice with only one husband?" Such an objection can only be raised by a base and extremely shameless woman who desires that she too should be allowed to marry four men at the same time. However, in Islam’s just law, if a man has four wives, there is no confusion in lineage, nor do any complications arise in matters of inheritance. In contrast, if a woman were to have relations with two men, the lineage would become doubtful, because lineage is connected to the man, not the woman. Complications would also arise in matters of inheritance.

If a woman were allowed to have four husbands, whose house would she live in? Who would be responsible for her maintenance and the expenses of her children? Let us consider this objection from another angle: just as sexual desire exists in humans, it also exists in animals. A man is permitted to have four wives, but if we look at dairy farmers, we see that they keep twenty buffaloes for milk, and there is only one bull among them. Has anyone ever seen a farmer keep twenty bulls and only one buffalo? Now, reflect for yourself: why does this happen, and why does it not happen the other way around?