Is a man's marriage to a woman during her iddah (waiting period) or one temporarily forbidden to him considered void, and does she become permanently forbidden to him?

The marriage of a woman during her iddah (waiting period) is invalid by scholarly consensus, based on the Almighty's saying: ﴿And do not resolve upon the knot of marriage until the prescribed term has reached its end﴾. The iddah is for ascertaining the emptiness of the womb. Scholars differed concerning whether she becomes permanently forbidden to the second husband. Some scholars held that she becomes permanently forbidden, such as the view of Malik and a narration from Ahmad, while Al-Shafi'i, in his new school of thought, permitted it after the completion of both waiting periods.

Some scholars mentioned that the matter is subject to the judge's discretion to rule for permanent prohibition as a disciplinary measure and deterrent if he deems it to be in the public interest. As for marrying women who are temporarily forbidden, such as a married woman, a non-scriptural disbeliever, the wife's sister, or her maternal or paternal aunt, or a fifth wife for someone who already has four wives, such marriages are invalid.

Scholars differed regarding marrying the wife's sister, paternal aunt, maternal aunt, niece (brother's daughter), or grandniece (sister's daughter), or a fifth wife for someone who has separated from one of his wives and she has become irrevocably divorced, while she is still in her iddah. The Malikis and Shafi'is permitted it, while the Hanafis and Hanbalis prohibited it until the iddah expires.