Question: While performing Isha with jamat, I had strong doubt as to whether I performed masah. I continued with the salah but cannot recall precisely why I continued. I think the main reason would have been that I did my wudhu and I am now too lazy to go again to perform masah so I may as well continue.
The second subsidiary reason was I vaguely recall I have been advised (not by you) to continue the salah and therefore a rationalised my laziness by consoling myself that I can’t have committed kufr? Would what I have described above constitute kufr?
Answer: What you have been advised with regards to continuing your salah in case of doubt is correct.
You should not pay too much attention to all the doubts that come to your mind. It is just another trick by which Shaytan seeks to lead you astray. You should try and dispel these doubts as much as possible.
The principle you should adhere to is:
اليقين لا يزول بشك
Certainty is not dispelled by doubt
As you were certain that you had performed wudhu, this certainty is not dispelled by doubting whether you had performed masah or not.
When we are driving, we just continue to do everything necessary, even though our minds would be somewhere else, similarly when we are doing any Ibadat, we continue to do what is necessary, even if we don’t realise, so you must have done masah.
By not returning you did the right thing, you did not commit any kufr. May Allah swt help you in getting rid of shak beemari.