If a person breaks a four-rakaat salah how many rakaats shall he do qadha

In the name of Allah, the most Beneficent, the most Merciful.

Answer

If one breaks a four rakaat fardh prayer such as Zuhr, Asr and Isha then one will be required to do qadha of four rakaats. The same rule also applies for a four rakaat Sunnat Muakkadah.

With regards to four rakaat nafl prayers or four rakaat ghair Sunnah Muakkadah then in principle one should be doing qadha of only two rakaats as each two rakaat is considered as a separate unit. However, Mufti Rasheed Ahmad Ludhianwi has written in his Ahsanul Fatawa that it is wajib to do qadha of four. The reason for this is because the second unit (i.e. third and four rakaat) were not performed thus one needs to do qadha of that. The first unit (i.e. first and second rakat) is incomplete as the salam was not performed and those prayers where any wajib acts are omitted one is required to repeat them. (Ahsanul Fatawa p.484 v.3) 

Only Allah Knows Best

Mohammed Tosir Miah

Darul Ifta Birmingham