Bukhari

Hadith Commentary:
That is, those who were not fasting received more reward than those who were fasting. It is understood from this that serving the mujahideen (those engaged in jihad) carries more reward than fasting. Fasting is an individual act of righteousness, but serving the mujahideen is service to the entire community; therefore, it is given precedence in any case. The meaning of the hadith is also that although fasting is pure goodness and a specific and accepted act of worship, still, in situations such as travel, where due to fasting there is a risk that other important tasks may be left undone, then not fasting is superior.
The incident mentioned in the hadith also presented this very situation: those who were fasting, due to fatigue and so on, were unable to perform any tasks, but those who were not fasting carried out all the services with full attention; thus, their reward surpassed even that of those who were fasting.

Hadith Commentary:
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Imam Bukhari rahimahullah has mentioned three hadiths under this chapter heading:
In the first hadith, the service of the elder by the younger is mentioned; in the second hadith, the service of the younger by the elder; and in the third hadith, the service of peers for one another is mentioned.
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From these hadiths, it is understood that serving the mujahideen at the time of jihad brings more reward than fasting, because those who broke their fast received the reward of their own action, and those who served the fasting ones received a reward equal to that of the fasting ones as well.
Since they served the fasting people and gave water to their mounts and provided fodder, they became more deserving of reward than the fasting ones.
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From these hadiths, it is also understood that serving one’s peers is permissible, and even serving someone younger than oneself is allowed.
Serving elders, of course, is a sign of noble character.

Hadith Commentary:
Vocabulary of the Hadith:
(a)
Tahazzama al-muftiroon:
Those who were not fasting girded up their loins.
(b)
They became ready and alert for service.
(c)
They adopted resolve and caution.
Benefits and Issues:
The fasting individuals, due to their weakness and frailty, were unable to perform even their own tasks, whereas those who were not fasting accomplished both their own work and the work of the fasting individuals. In this way, by serving the fasting people, they earned greater reward.

(1) To observe voluntary fasts (nafl) during travel with such hardship that the fasting person cannot even perform his own tasks and others have to do his work for him is not preferable. Fasting during travel is preferable only when a person does not become incapacitated and does not become a burden upon others.

(2) “They took the reward.” That is, the reward of service. Generally, this phrase is used in the context of preference, as if on that day those who did not fast surpassed those who fasted. And Allah knows best.

(3) Assisting one another in jihad is a deed of great reward.