Question :

What should a praying person who doubts having offered one, or two prostrations in the third Rakah (unit of prayer) do?

The Answer :

Whoever has doubts about their prayer should consider what is less i.e. the above person should offer another Sajda (prostration) and complete his/her prayer, then offer Sujood As-Sahw (prostration of forgetfulness). And Allah Knows Best.