Q: In the Hanafi madhab, if you remain silent (during prayer) for a time period where one can recite "Subhan Allah" 3 times, then it becomes waajib for the person to perform Sajdah Sahw. If, however, the individual did not perform Sajdah Sahw, does he then have to repeat his prayer? What if, in the past, the person did not pay attention to this fact during his prayer, and he now has several prayers where he was required to perform Sajdah Sahw, but he did not do so. Does he have to repeat all those prayers?