Answered by Sidi Salman Younas
Question: I didn’t know that in case when one doubts whether he’s performing the 3rd or the 4th rakaat, he should perform at-tahiyyat in this and in the following rakaats. So I used to perform the 3rd and the 4th rakaats with only one at-tahiyyat at the end of the 4th rakaat in such cases. Should I make qadha of all such prayers now?
Answer: I pray you are well.
No, you will not be required to make up any of your prayers in this situation.
There are two possible scenarios when someone doubts what cycle (rak`at) of the prayer one is in:
a. It is the first time that such a doubt occured to the person in his life,
b. It is not the first time that such a doubt occured to the person in his life.
If it is the first case, one should restart his prayer.
If it is the second case, then one should take a brief moment [while still continuing the actions of the prayer or reciting something] to quickly recall what cycle one is in and then make a reasonable guess. If someone does so, then the prayer should be completed based on the reasonable guess the individual made. Thus, for example, if a person has doubts between whether he is in the third or fourth cycles of the prayer and, after thinking, he decides that he is in the fourth cycle, he should simply finish that cycle, sit down for the final sitting, and complete his prayer. No forgefulness prostration is needed in this case.
In your situation, it would seem that by not sitting for the tashahhud in the third cycle, you already exercised your judgment as to what cycle you were in. Therefore, you can ignore all your previous doubts and should not worry about making up those prayers.
In the future, if such a doubt occurs, then remember that to decide what cycle you are in you do not need to be completely certain. All you have to do is make a reasonable guess and then build your prayer on that.
[Ibn `Abidin, Radd al-Muhtar]
Checked & Approved by Faraz Rabbani