My father answered that at the time of prophet Muhammad, (peace of Allah be upon him), there were many wars and many men were killed. As a result the number of men was much less that the number of women. Because of the mercy of Allah upon women who had no one to marry them, he allowed each man to marry up to four women. I said to my father, “But there are no wars now”.  He responded, “See, I am married to one woman only and among our big family, no man married more than one woman. Do not worry, marrying more than one woman happens very rarely and only among the uneducated”.


Bukhari
Volume 7, Book 62, Number 6:
Narrated Anas:
The Prophet I used to go round (have sexual relations with) all his wives in one night, and he had nine wives.

Volume 7, Book 62, Number 142:
Narrated Anas bin Malik:
The Prophet used to pass by (have sexual relation with) all his wives in one night, and at that time he had nine wives.

Volume 7, Book 62, Number 17:
Narrated Jabir bin 'Abdullah:
When I got married, Allah's Apostle said to me, "What type of lady have you married?" I replied, "I have married a matron' He said, "Why, don't you have a liking for the virgins and for fondling them?" Jabir also said: Allah's Apostle said, "Why didn't you marry a young girl so that you might play with her and she with you?'

Volume 7, Book 62, Number 48:
Narrated Hisham's father:
Khaula bint Hakim was one of those ladies who presented themselves to the Prophet for marriage. 'Aisha said, "Doesn't a lady feel ashamed for presenting herself to a man?" But when the Verse: "(O Muhammad) You may postpone (the turn of) any of them (your wives) that you please,' (33.51) was revealed, " 'Aisha said, 'O Allah's Apostle! I do not see, but, that your Lord hurries in pleasing you.' "