Is the prostration of forgetfulness (sujud al-sahw) obligatory for the worshipper if he doubts having omitted a obligatory act, then becomes strongly convinced that he did perform it, and when would that be? And is it obligatory for him if he doubts having omitted a obligatory act, then becomes absolutely certain that he did perform it, and when would that that be?

Whoever doubts having omitted an obligatory act, then his doubt vanishes and he ascertains that he did perform it, is not required to perform the prostration of forgetfulness (sujud al-sahw). Similarly, whoever doubts having omitted an obligatory act, then it becomes highly probable to him that he did perform it, is not required to perform the prostration of forgetfulness, due to following the dominant probability. However, if it becomes highly probable to him that he did not perform it, then he must perform the prostration of forgetfulness, and it should be done before the salutation (taslim), because it is due to a deficiency.