Some are prescribed at specific times, while others are not fixed to any particular time.
Some are tied to a particular cause, while others are not tied to any cause.
All of them are referred to as voluntary prayers.
The most emphatic of the voluntary bodily acts of worship is jihad. It has also been said: seeking knowledge.
The correct view is that this varies according to the person performing it and according to the time. Thus, we may say to one person: jihad is best in your case; and to another: seeking knowledge is best in your case. If a person is brave, strong, and energetic, but not particularly intelligent, then jihad is best for him, because it is more suited to him. But if he is intelligent, has a strong memory, and is forceful in argument, then seeking knowledge is best for him. This is with respect to the individual concerned.
With respect to the time, if we are living in an age in which ignorance and religious innovations have become widespread, and many people issue legal rulings without knowledge, then seeking knowledge is better than jihad. But if we are living in an age in which scholars are numerous, while the frontiers need those stationed there to defend the Muslim lands, then jihad is best. If there is no factor giving preference to either of the two, then seeking knowledge is best.
Imam Ahmad said: “Nothing is equal to knowledge for one whose intention is sound.” They asked, “How can one’s intention be sound?” He replied, “He intends humility and to remove ignorance from himself.” This is correct, for the whole foundation of the Sacred Law is knowledge; even jihad is founded upon knowledge. This is indicated by the saying of Allah, Most High:
“It is not for the believers to go forth all together. So why should not a group from every division among them go forth to gain understanding of the religion and to warn their people when they return to them?” [al-Tawbah: 122]
Thus, Allah ruled out the Muslims’ all going forth for jihad; rather, one group should go forth while another group remains.