Answer
(Fatwa: 381/281/L=1432)
It is obligatory on you to offer all those salah that you have missed unknowingly. First, you should calculate all the missed salah. For example, you have missed two or three years’ salah, make the qaza of three years and include witr in qaza salah as well with the five daily salah. The easy method of qaza salah is to make the qaza of one or two salah with each salah time and note down it in any notebook to remember it. You should make this intention at the time of doing qaza that you are offering the first or last salah of Fajr or Zuhar of all your missed salah.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband