Whoever marries his father's wife is to be beheaded

It is narrated from Sayyiduna al-Bara bin Azib (may Allah be pleased with him) that he said: I was searching for my lost camels and was wandering around the houses of the settlement when suddenly I came upon a band of riders. The people of the settlement began seeking refuge at my house. Then those riders surrounded my courtyard and brought a man out of it. They did not speak to him or ask him anything, but (immediately) struck off his head. When they left, I asked about him, and the people told me that he had married his father's wife (widow or divorcee).
This hadith has an authentic chain (sahih al-isnad), but the two Shaykhs (Bukhari and Muslim) did not record it, and the hadith of Yazid bin al-Bara is a supporting witness (shahid) for it.

It is narrated from Sayyiduna al-Bara bin Azib (may Allah be pleased with him): I met my paternal uncle, who had (a special) banner with him. I asked: Where are you heading? He said: The Prophet (peace and blessings be upon him) has sent me to a man who has married his father's wife; he (peace and blessings be upon him) ordered me to strike off his head and take possession of his wealth.

It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The thing I fear most for my Ummah is the act of the people of Lut (sodomy)."
This hadith has an authentic chain (sahih al-isnad), but the two Shaykhs (Bukhari and Muslim) did not record it.