Mustadrak al-Hakim — Hadith 2842

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that a man asked him about a man who had divorced his wife with three pronouncements, after which his brother married her, without any (prior) consultation with him, merely with the intention of making her lawful for his brother: would she be lawful for the first husband? He said: "No, unless it is a marriage of genuine desire. In the blessed time of the Messenger of Allah (peace and blessings be upon him) we used to regard such a thing as fornication (sifah)."
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.