What is the criterion for the ability to perform jihad?

The questioner : The one who is able...

The Shaykh : How?

The questioner : The one who is able to perform jihad...

The Shaykh : The ability, my brother, varies from person to person, and it is not specific to jihad; it applies to everything. For example, the Messenger of Allah said: Who is it that judges whether a given person is able to pray standing or not able to? The doctor does not judge for him; rather, he judges for himself. So how much more so is this the case with a matter that has many branches related to the one who is said to be able to fight in the cause of Allah or not able to? This is a matter in which he judges for himself. Recently, we gave two examples that are as far apart as possible, and between them are examples by the dozens, if not hundreds; because the issue differs from one to another by a hair's breadth.
The first example: A young man is the only one available to two elderly sheikhs who have no one to attend to their essential needs but him. So is he said to be able or not able? We are bound by the rule, but considering that if he left them and went out to fight in the cause of Allah, he would neglect them; meaning, in the course of fulfilling an approaching obligation, he would neglect an existing, realized obligation, which is serving his parents.
The other example, which is the opposite of this: Two young, energetic parents have been blessed by Allah with children. So if one of them goes out to fight in the cause of Allah, they do not feel any deficiency in their service or in what is obligatory for their children to do for them. So how much more so if this individual, this one son, goes out in the cause of Allah? Here it becomes apparent that he is able to fight in the cause of Allah.
Look at these two examples, which are far apart from each other. But I return to this latter one; this latter one may find that he is not permitted to go out. He is not a bird that flies; he is a human being who walks on the face of the earth. So he was not able to travel, but from what aspect? Not from the aspect of his inability being related to his parents? No, from this angle he is able. Because of these subtleties in matters related to a person and a person's ability, whether negative or positive, it is not permissible for anyone to say that so-and-so is able or not able. Rather, the matter is as He, the Exalted, said:
Other than that?