Sunan An-Nasa'i 3411--It was narrated from Anas, that the Messenger of Allah had a female slave with whom he had intercourse, but Aishah and Hafsah would not leave him alone until he said that she was forbidden for him. Then Allah, the Mighty and Sublime, revealed: "O Prophet! Why do you forbid (for yourself) that which Allah has allowed to you" [66:1] until the end of the verse.
So let's follow the chain of events.
(1) Surah 4:3 declares that Muslims may have up to four wives.
(2) Muhammad receives Surah 33:50, which gives him (and him alone) the right to have even more wives.
(3) Various verses in the Qur'an declare that Muslim men may have sex with their slave-girls and female captives.
(4) Muhammad (who already had nine wives who were incredibly jealous of one another) chooses to have sex with his slave girl.
(5) Two of his favorite wives were extremely upset by this, and they compel him to stop his adulterous affair.
(6) Allah tells Muhammad, in effect, "Why are you listening to your wives? Didn't I tell you that you are free to have sex with your slave girls?"
Thus, Muhammad's wives simply had to accept the fact that he was free to have sex with his beautiful slave girl (just as they had to accept the fact that he was free to show favoritism among his wives). If Allah has no concern for the feelings of the Mothers of Believers, should we expect him to be concerned about the feelings of other women?