If we make a mistake in Sajdah Sahw for example we do not place our nose firmly on the ground we just touch it a little bit, do we have to do Sajdah Sahw again? If we make a mistake after Sujood Sahw when we make salaam do we have to do repeat?
In the name of Allah, the most Beneficent, the most Merciful.
” He is to prostrate on his nose and on his forehead, because the Prophet did so persistently. If he confines himself to prostrating on one of these, it is valid according to Abu Hanifah .The two jurists have said (Imam Muhammad and Abu Yusuf ) it is not proper to prostrate on the nose alone , except due to an obstacle” (Al Hidayah The book of Prayer p.108 v.1 )
We learn from the above text in Hidayah that to place your nose on the ground in sajdah is a must and the only time you can confine on one is when you have a valid reason.
With regards to your first question if your nose was placed on the ground regardless of whether it was placed firmly or not then your sajdah will be done, so long as your nose is on the ground and Sajdah Sahw will not be necessary.
With regards to your second question, if the mistake was such that you omitted a Fard then your salah will be invalid, for example you missed out a Sajdah (which is fard), the same would apply if you missed out a Waajib act intentionally for example you deliberately did not read tashahud , (yes if a Waajib act was missed unintentionally then one sajdah sahw will suffice) however if you missed a Sunnah or a Mustahab act like tasbeeh whilst in Ruku and Sujood etc then your salah will be valid and Sajdah Sahw will not be necessary.
Only Allah Knows Best
Written by Molana Ishaaq Hussain
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham.