All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
This Hadeeth is reported in Saheeh Muslim, and the tribe conquered by Abu Bakar was Fazaarah. It should be noted that the Islamic Sharee’ah and its tolerance with war prisoners and treatmenting them kindly, far exceeded all legislations. The guidance of the Prophet was that he urged the people to honor them and be kind to them, pursuant to the teachings of the Quran, as Allah Says (what means): {And they give food in spite of love for it to the needy, the orphan, and the captive.} [Quran 76:8]
Abu Moosa Al-Ash’ari narrated that the Prophet said: “Set the captives free, accept the (food) invitation, and visit the ill.” [Al-Bukhari]
There is nothing in the Hadeeth that suggests what was mentioned in the question that the Prophet gave permission to Salamah to rape the woman for one night...etc. This is nothing but a pure lie. Rather, the reality is what Abu Salamah himself mentioned in this Hadeeth, as he said: “I did not uncover her dress.” Ash-Shawkaani said: “This is a metaphor that he did not have intercourse with her.” [End of quote]
Islam forbade separating between a woman and her child who has not yet reached the age of puberty. Ibn Qudaamah reported the consensus of the scholars on this issue. Their evidence is the Hadeeth narrated by Abu Ayoob who said: “I heard the Prophet saying: “Whoever separates between a mother and her child, then Allah will separate between him and his beloved ones on the Day of Judgement.” [At-Tirmithi]
In one of his views, Imam Ahmad said that the adult is like others [i.e. like the one who did not reach puberty]. Ibn Qudaamah said in Ash-Sharh Al-Kabeer:
“There is no difference between the child [whether a boy or a girl] being an adult or a minor [not yet reached puberty] as per the apparent view of Al-Khiraqi and one of the two views reported from Ahmad based on the general meaning of the text in this regard. This is because the mother is harmed by being separated from her adult son; it is for this reason that he (the son) is forbidden from going to Jihaad except with her permission.” [End of quote]
The Hadeeth you asked about in the question does not prove that the Prophet separated between the girl and her mother. If we presume that this is confirmed, it is interpreted to mean that the girl had reached the age of puberty. It is for this reason that Mubaarak poori said in Tuhfatul-Ahwathi:
“It seems that the girl had reached the age of puberty....” [End of quote]
As we know, the adult can take care of himself and does not need the help of his mother; this is something that we witness in our real-life.
We warn our Muslim brothers who are not well-versed in Islamic knowledge against following the misconceptions of the enemies as these misconceptions may be a reason that would lead them to doubt their religion. The following is a useful advice by the prominent Imam Ibn Al-Qayyim in his book Miftaah Daar As-Saʻaadah (Key to the Abode of Bliss):
“Shaykh Ibn Taymiyyah said to me when I started to report to him one misconception after another, 'Do not make your heart, when exposed to such trials, absorb it like a sponge absorbs water, rather let it be like an impermeable glass vessel, misconceptions pass over it but do not settle in it. Such a vessel sees the misconception with its [the vessel's] clearness but repels it [misconception] with its firmness. Otherwise, if your heart absorbs every misconception that passes by it, then, in that case, your heart becomes a settling place for misconceptions,' or as he said. I do not think that I have ever benefitted from any advice in repelling misconceptions more than I benefitted from this advice. A misconception is called as such because the truth is confused with falsehood in it, as it makes the garment of the truth cover the body of falsehood…” [End of quote]
Allah knows best.