Nasai

Urdu marginal note:
"Musalsal" (continuous) means that from the time he sets out for jihad until his return, a person remains constantly in the state of fasting and prayer, without showing laziness even for a moment. Clearly, this is not possible. Thus, there is no other deed equal to jihad. Or, whatever reward may be supposed for such a hypothetical situation, that reward will be given to the mujahid, provided that he is performing jihad purely for the sake of Allah (lillahi ta‘ala).

Hadith Commentary:
That is, the true state of intention is best known to Allah alone—whether a person is sincere or not. If he is sincere, then he is a true mujahid; otherwise, if someone fights for worldly wealth, status, or fame, he is not a mujahid in the path of Allah (fi sabilillah).

In the example, performing prayer refers to voluntary (nafl) prayer, and fasting refers to voluntary (nafl) fasting—that is, a person who spends the entire day in voluntary fasting and the entire night in voluntary prayer. The rank of the mujahid is even higher than this.

Hadith Commentary:
➊
Allah, the Exalted, has guaranteed for the mujahid that if he is martyred, He will admit him into Paradise immediately after his death.
And if he does not die in the path of Allah but rather returns safely, then Allah, the Exalted, will grant him reward and spoils of war. It is not possible that in the case of his safe return he receives nothing; rather, he will receive both spoils and reward, or at the very least, he will certainly receive one of them.
➋
From this hadith, it is also understood that the reality of intention is known only to Allah, the Exalted. If he is sincere, then he is a mujahid; but if he is not sincere, and instead enters the battlefield for worldly wealth or his own fame, then he is not a mujahid in the path of Allah, nor is he entitled to any kind of reward with Allah. Furthermore, it is also known that not a single moment of the mujahid in the path of Allah is devoid of reward, as is stated in the noble verse:
﴿لَا يُصِيبُهُمْ ظَمَأٌ وَلَا نَصَبٌ وَلَا مَخْمَصَةٌ فِي سَبِيلِ اللَّـهِ وَلَا يَطَئُونَ مَوْطِئًا يَغِيظُ الْكُفَّارَ وَلَا يَنَالُونَ مِنْ عَدُوٍّ نَّيْلًا إِلَّا كُتِبَ لَهُم بِهِ عَمَلٌ صَالِحٌ ۚ إِنَّ اللَّـهَ لَا يُضِيعُ أَجْرَ الْمُحْسِنِينَ ﴿١٢٠﴾ وَلَا يُنفِقُونَ نَفَقَةً صَغِيرَةً وَلَا كَبِيرَةً وَلَا يَقْطَعُونَ وَادِيًا إِلَّا كُتِبَ لَهُمْ لِيَجْزِيَهُمُ اللَّـهُ أَحْسَنَ مَا كَانُوا يَعْمَلُونَ)
“The mujahideen, whatever hardship of thirst, fatigue, or hunger they endure in the path of Allah, or any place they tread that angers the disbelievers, or any achievement they gain over the enemy, a righteous deed is written for them because of it. Allah does not let the reward of the doers of good go to waste. And whatever they spend, small or great, or any valley they cross, it is written for them, so that Allah may reward them with the best of what they used to do.” (al-Tawbah 9:120-121)
That is, for every action of the mujahid during the journey of jihad, a righteous deed is written in his record of deeds, whether that action is voluntary or involuntary. For all these actions, he will receive reward with Allah.

Hadith Commentary:
Benefits and Issues:
It is a very difficult task for a person to always fast during the day, stand in prayer at night, and spend his entire life in obedience through all kinds of hot and cold, good and bad circumstances, without showing any kind of laziness or negligence. However, by sincerely engaging in jihad, he attains this rank, even though fighting is not taking place at every moment and in every situation there.

English translation:

"Allah knows best," because intention is a hidden matter. People only see the outward; Allah, however, sees the heart as well. Only that person will attain virtue who goes out for jihad purely for the sake of Allah. If any other impurity enters into it, then this jihad, instead of leading to Paradise, can become a means to Hell.