Mustadrak al-Hakim — Hadith 3750

Sayyiduna Abdullah bin Buraydah narrates from his father that he said: I was sitting with Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) when he heard the voice of a woman crying out. He said: "O Yarfa', see what this voice is." He went, looked, came back and said: "It is a girl of Quraysh whose mother is being sold." At this Sayyiduna Umar (may Allah be pleased with him) said: "Call the Muhajirun and the Ansar to me." The narrator said: Only a short while had passed before the house and the room were full. Then Sayyiduna Umar (may Allah be pleased with him) praised and extolled Allah, and said: "To proceed: Do you know whether severing the ties of kinship was part of what Muhammad (peace and blessings be upon him) brought?" They said: "No." He said: "Yet it has become widespread among you." Then he recited this verse: "Then would you perhaps, if you were given authority, cause corruption on the earth and sever your ties of kinship?" [Surah Muhammad: 22]. Then he said: "What severing of kinship could be greater than that the mother of a man among you should be sold, when Allah has granted you abundance?!" They said: "Do whatever you see fit." So Sayyiduna Umar (may Allah be pleased with him) had it written to all the regions that the mother of a free man is not to be sold, for it is severing of kinship and it is not lawful.
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.