Shaykh al-Islām—may Allah have mercy on him—said:

People disagree over whether commanding something also entails commanding its necessary requirements, and whether it entails prohibiting its opposite, although they agree that the commanded act cannot be performed without fulfilling its necessary requirements and refraining from its opposite. (*)

The disagreement arises because someone who commands an act may not intend its necessary requirements or the avoidance of its opposite. Thus, if he punishes the legally accountable person, he punishes him only for failing to perform the commanded act, not for omitting its necessary requirements or doing its opposite.

This issue is commonly expressed in the maxim: “Whatever is indispensable to fulfilling an obligation is itself obligatory.”

Some people have erred in this matter by dividing such requirements into two categories: those beyond the legally accountable person’s ability, such as soundness of the limbs, the requisite number of participants for Friday prayer, and similar matters that he cannot secure; and those within his ability, such as travelling the distance required for Hajj, washing a portion of the head during ablution, observing the fast for part of the night, and similar matters.

They therefore said: “Whatever is indispensable to fulfilling an unconditional obligation, and lies within the legally accountable person’s ability, is itself obligatory.”