Is a man's prayer valid if he prays in the mosque and then leads his wife in prayer at home in any of the following cases: Fajr prayer, two rak'ahs for both of them; Dhuhr, Asr, or Isha prayer, four rak'ahs with the intention of Sunnah for both of them; or two rak'ahs for him, and then he says the taslim, and she completes her prayer?

It is permissible for a woman to pray Fajr behind her husband while he is praying the two rak'ahs of Fajr [Sunnah (definition)]. It is also permissible for her to pray Dhuhr, Asr, or Isha behind him while he is praying the pre-prayer Sunnah. Furthermore, it is permissible for her to pray a four-rak'ah obligatory prayer behind him while he is praying two rak'ahs of a supererogatory prayer, and then after he says the taslim (definition), she completes her prayer. This is based on the Shafi'i school of thought.