Yahya bin Zakaria bin Abi Zaida يحيى بن زكريا بن أبي زائدة · The Book of Marriage

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

"The Messenger of Allah forbade Ash-Shighar." (One of the narrators) 'Ubaidullah said: "Ash-Shighar means when a man gives his daughter in marriage on condition that (the other man) gives him his sister in marriage."