If a person’s wudhu is nullified during sajdah sahw, what should that person do?
In the name of Allah, the most Beneficent, the most Merciful.
Imam Shafi (RA), Imam Malik (RA), Imam Ahmad Bin Hanbal (RA) and Imam Abu Yusuf (RA) are of the view that to end the salah with salaam is fardh. If a person finished his salah without the salam then his salah would not be done.
However, Imam Abu Hanifah (RA) is of the view that to recite or to sit up to the end of tashahud is fardh and to end the salah with salam is only wajib.
Therefore, if one broke his salah after the tashahud through actions, which contradict the validity of salah, such as talking or turning, away from the Qiblah (known as Khuruj Bi Sunihi) the salah will be valid but it will be obligatory to repeat the salah during its time. (Dars Tirmizi p.495 v.1)
With regards to your question it will be wajib (obligatory) to repeat your salah as you have omitted the Salaam, which is wajib in the Hanafi Fiqh. If you do not repeat the salah, the obligation of the salah will be done as in the Hanafi Fiqh Khuruj Bi Sunihi is compulsory.
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.