Sajda-e-Sahw

Q: I have read the Hadiths regarding sajda sahw. My question is that (shia asked me) can a Nabi forget?

Q: I was leading jamat at Maghrib. In the second standing, I forgot to recite aloud.  By the time someone said SubhanAllah, I was halfway in Fatiha. Upon realising the mistake, I recited Fatiha aloud from the start (repeating first half quiet and then loud). My question is, what portion of Fatiha can be repeated without sajdah-e sahwa becoming wajib?

Q: If I am the Imaam in maghrib salaah and I mistakenly read the qiraat softly, should I repeat the qiraat loudly? Also, is it necessary for me to perform sajdah-e- sahw?

Q: I was praying and I got doubts about how many sajdahs I did and I was doing first the Tashahhud and I determined that I would do one more sajdah in case and I was reciting "Assalaamu alayka ayyuhannabeyyu.. " and around here or after "wa" I determined that I was going to do sajdah, but I added "wa Rahmatullaah" and then I stopped and proceeded to do sajdah (I did Sajdah-Sahw afterwards). But now I doubt that I did an "addition" that invalidates the salaah.

Q: In Jalsa, I mistakenly recited approximately half of the duaa in Janaazah salaah for an adult. I was a munfarid.

(1) I made Sajda Sahw. Is this sufficient?

(2) Must I repeat the Salaah?

Q: A person is performing Salaah reading his dhor and he forgets where he is. He thinks for a few seconds and goes back and continues. Does this pause make sajdah sahw necessary?

Would this change depending on the Salaah he was performing e.g. if it were sunnats or taraweeh or fardh etc?

Q: If in salah on my own, I am reciting out loud and I recite bismillah out loud, and half way through it I stop, and re-recite it silently, is my salah invalidated? Also, is it invalidated if I recite it out loud and complete the recitation of it out loud only to re-recite it silently? I also have the same question but instead of Bismillah, I recite ameen out loud. Does reciting ameen out loud invalidate the prayer? also, if it does, would rectifying the ameen out loud by reciting it again straight after silently, cause the prayer to be valid again? Another question I have is that during the salah, I said some of the takbeers out loud and others including possibly 'Sami Allahu liman hamida' silently. Would this inconsistency render my salah invalid?

Q: I was wondering if sajda sahw is necessary when one enters into jalsa and before putting his hands on his thighs, begins saying 'allahuma aghfirlee wa arhamnee', putting them on his hands during the recitation of the dua. Also, if the back is not completely straight during rukoo, then is the salah invalidated?

Q:

1. If a person reads the ruku tasbeeh in sajda and due to the mistake he makes a sajda sahwa, is the salah valid?

2. How many sajda tasbeehs can a person read in tahajjud salaah?

Q: What to do if I pray three rakaats Salaah in asr by mistake? Should I have to repeat the namaaz or sajdaa sahu will be enough to complete the namaz? Also if I forget which rakaat I am in, then what should I do?