Sajda-e-Sahw

Q: Can you please explain uptil when sajda-e-sahw can be done for unintentionally missing out a wajib in the prayer? If a person unintentionally leaves out a wajib, and they have done salaam, can they still do sajda-e-sahw? Also, if a person does not do sajda-e-sahw, and the prayer time has ended, will they have to redo the prayer? I have heard that the prayer will have to be redone for leaving out a sajda-e-sahw as long as its still the prayer time, but after the prayer time has passed, it is not mandatory to redo the prayer, but recommended to. Please if you can explain.

Q: My question is, in asar namaaz, if the Imam forgets to perform qada-e-ula and stands, after the interruption of Muqtadi he sits again in qada. During qada ukhraa he performs sajda e sahw. Is the namaz correct or not?

Q: I performed the four sunnah of Asr salaah however in the 3rd rakaat I forgot to read a Surah after Surah Fatiha only realised this in ruku. I intended to make sajda sahwa but after the 4th rakaat I read the tashahud, durood and dua and made both salaams. Whilst making the second salaam I remembered the sajda-e-sahw and immediately made a sajda after then completed the Salaah. Was I correct or did I have to repeat the Salaah?

Q: If a masbooq makes such an error (that causes sajda sahw to be made) in the rakats he missed with the imam, should he make sajda-e-sahw or not?

Q: I lead Maghrib prayer. There were two muqtadees. I recited Surah Fatiha 's begining verses without voice. I will inform one of them to repeat his prayer but I don't know where the other one is. What should I do?

Q: If the Imaam prays Surah Fatiha silently in jahri salaat, would sajda-e-sahw be wajib? If only two verses or three verses are recited what will be the Hukm?

Q: It sometimes happens that while offering four rakaats namaz, I get confused whether I am in the third or fourth rakaat, so I either pray the whole namaz again or conclude that I am offering the third rakaat and offer one more rakaat, do sajdah-e-ahw and finish my namaaz. I want to know if I get confused regarding the rakaat, then what has to be done?

Q: If a person misses sajdah-e-tilaawah while performing salaah e.g. he was reciting a surah which had a verse of sajdah, but he did not remember to perform the sajdah, is he required to repeat the salaah? 

Q: If a masbooq makes both salaam after the salaah concluded, will sajdah sawh suffice or will the person have to repeat the salaah?

Q: My question is regarding sajdah-e-tilaawah during salaah. If I mistakenly performed two sajdahs instead of one, what should I do?