Hajjaj bin al-Minhal حجاج بن المنهال · The Book of Divorce

"The Prophet was asked about a man who divorced his wife three times, then another man married her and he closed the door and drew the curtain, then divorced her before consummating the marriage with her. He said: "She is not permissible for the first one (to remarry her) until the second one has had intercourse with her.""

A similar report was narrated from Safiyyah bint Abi 'Ubaid from one of the wives of the Prophet -and she is Umm Salamah- from the Prophet.