[Abu 'Eisa said:] This Hadith is Hasan Gharib. Some of the people of knowledge among the Companions of the Prophet (ﷺ) and others, disliked separating between the captives when selling them.
Some of the people of knowledge permitted separating the children that were born in the land of Islam, but the first view is more correct. It has been related that Ibrahim An-Nakha'i seperated a mother and her child in a sale, so he was asked about that. He said: "I sought her permission for that and she approved."
In-book : Book 14, Hadith 86
English translation : Vol. 1, Book 12, Hadith 1284