Amr bin Mnswr al-Nsa'iy عمرو بن منصور النسائي أبو سعيد · The Book of Marriage

"The Prophet married Maimunah when he was a Muhrim."

"We have been saying that you want to marry Durrah bint Abi Salamah." The Messenger of Allah said: "As a co-wife to Umm Salamah? Even if I were not married to Umm Salamah, she would not be permissible to me, for her father is my brother through breast-feeding."

"I was thinking of forbidding Ghilah until I remembered that it is done by the Persians and Romans" -(one of the narrators) Ishaq said: "(They) do that -and it does not harm their children."

It was narrated from Ibn 'Umar that the Messenger of Allah forbade Ash-Shighar. Ash-Shighar means when a man marries his daughter to another man, on the condition that that man marries his daughter to him, and no dowry is exchanged between them.

"The Messenger of Allah said: 'What differentiates between the lawful and the unlawful is the Duff, and the voice (singing) for the wedding.'"