Brother if I started a prayer during its time and the azan for the next prayer starts during my prayer like say, the fourth rakat, will my prayer which I was praying before the time ended be valid or qaza? Jazak'Allah Kher.
Such situation will only arise if you are neglectfull of the timings of the prayer. However if you have started a fardh prayer and before you finish the time of the other prayer starts then these two things can apply
1. either your whole prayer will be considered as Qaza ( that means the sawaab will be very very less )
2. Only the sawaab of the portion of the prayer performed after the time of next prayer starts will be considered as qaza and sawab will be average.
3. The whole prayer is counted as normal and sawaab will be full.
In the absence of hadith on the above topic -we cannot give you a definite reply. So please do not delay and pray at the first instance.