Nasai

Hadith Commentary:
The Messenger of Allah (sallallahu alayhi wa sallam) used to fast on the day of Ashura in Makkah al-Mukarramah. When he migrated to Madinah, he saw that the Jews also fasted on this day. When he inquired about the reason, it was explained that on this day, the Jews were saved from Pharaoh, so they fast on this day as a day of gratitude. The Messenger of Allah (sallallahu alayhi wa sallam) said: "We have a greater connection to Musa (alayhis salam) than they do." Then he (sallallahu alayhi wa sallam) observed this fast and instructed others to do so as well. (Sahih al-Bukhari, Kitab al-Sawm, Hadith: 2004)

And in the year in which he (sallallahu alayhi wa sallam) passed away, he said: "If I remain alive till the next year, I will also fast on the ninth (along with Ashura), so as to differ from the Jews." But before Ashura came, he (sallallahu alayhi wa sallam) passed away. (Sahih Muslim, Kitab al-Siyam, Hadith: 2666(1134))

Hadith Commentary:
There is a difference of opinion among the Salaf on this issue. Some have said that if one fasts while traveling, the obligatory fast will not be fulfilled and it must be made up later. The majority of scholars, such as Imam Malik, Shafi'i, and Abu Hanifah rahimahumullah, say that fasting while traveling is superior if one has the strength and there is no hardship. Our Imam Ahmad ibn Hanbal, al-Awza'i, Ishaq, and the Ahl al-Hadith say that not fasting while traveling is superior. Some have said that both are equal—whether one fasts or breaks the fast. Some have said that whichever is easier is superior.
(Wahidi)
Hafiz Ibn Hajar has explicitly stated that Hamzah ibn Amr radi Allahu anhu did not ask regarding voluntary (nafl) fasting, but rather about the obligatory fasts of Ramadan itself. The Messenger of Allah sallallahu alayhi wa sallam said: "It is a concession (rukhsah) from Allah, so whoever takes it, it is good, and whoever prefers to fast, there is no sin upon him."
(Fath al-Bari)
That is, the Prophet ﷺ replied to him that this is a concession from Allah; whoever accepts it, it is better, and whoever prefers to fast, there is no sin upon him.
The honorable scholar rahimahullah states that the word "rukhsah" (concession) is used in contrast to obligation (wajib). This is stated even more explicitly in the narration of Abu Dawud and al-Hakim, where he (Hamzah) said that he is often traveling and the month of Ramadan comes upon him while he is in a state of travel. In response to this question, the Prophet ﷺ gave the answer mentioned above.

Hadith Commentary:
(1)
Although there is no explicit mention of obligatory fasting in this narration, it is found in Sahih Muslim that Hazrat Hamzah Aslami radi Allahu anhu submitted:
O Messenger of Allah! I have the strength to fast while traveling; if I fast, will there be any sin upon me? Upon this, the Messenger of Allah sallallahu alayhi wa sallam said:
“This is a concession (rukhsah) from Allah; whoever accepts it has done well, and whoever prefers to fast, there is no harm upon him.” (Sahih Muslim, Kitab al-Siyam, Hadith: 2629(1121))
Hafiz Ibn Hajar rahimahullah states:
Rukhsah is used in contrast to obligation (wajib).
From this, it is understood that he had asked regarding the fasts of Ramadan.

(2)
It should be clear that in the hadith, what is meant by continuous fasting is not the fasting of wisal (continuous fasting without breaking the fast at sunset), because the Messenger of Allah sallallahu alayhi wa sallam has prohibited that.
(Fath al-Bari: 4/229)

Benefits and Issues:
In any journey during which it is permissible to shorten the prayer (qasr), it is also permissible for the traveler to break the fast, whether the journey is on foot or by riding, and whether the means of transport is a vehicle, airplane, etc., and whether there is fatigue that makes fasting difficult or there is no fatigue, whether there is hunger and thirst during the journey or not. This is because the Shari’ah has granted absolute permission to shorten the prayer and break the fast during such a journey, and has not placed any restriction regarding the type of transport, fatigue, hunger, thirst, etc.

The noble Companions (radi Allahu anhum) traveled with the Prophet (sallallahu alayhi wa sallam) during Ramadan for the purpose of jihad; some of them fasted and some did not. No one objected to the other regarding this. However, if due to intense heat, difficulty of the route, distance, and continuous travel, fasting becomes difficult, then the emphasized ruling for the traveler is that he should not fast, as is narrated from Anas (radi Allahu anhu): “We were with the Messenger of Allah (sallallahu alayhi wa sallam) on a journey. Some of us fasted and some did not. Those who did not fast were lively and did work, while those who fasted became weak and could not do some tasks. So the Prophet (sallallahu alayhi wa sallam) said: ‘Today, those who did not fast have taken the reward.’”
(Sahih al-Bukhari, Book of Jihad, Hadith: 2890; Sahih Muslim, Book of Fasting, Hadith: 119)

Sometimes, due to an emergency situation, it even becomes obligatory not to fast during travel, as is narrated from Abu Sa’id al-Khudri (radi Allahu anhu): “We traveled with the Messenger of Allah (sallallahu alayhi wa sallam) towards Makkah, and when we camped at a place, he said: ‘You have come close to your enemy, and breaking the fast will give you strength.’ This was a concession, so some of us fasted and some did not. Then, when we camped at another place, he said: ‘You are about to encounter your enemy, and breaking the fast will give you strength. Therefore, break your fast.’”
(Sahih Muslim, Book of Fasting, Hadith: 1120)

Since this was an emphatic command from him, all of us broke our fast. The narrator of the hadith states that after this, we also fasted during journeys with the Messenger of Allah (sallallahu alayhi wa sallam).

Similarly, it is narrated from Jabir (radi Allahu anhu) that the Messenger of Allah (sallallahu alayhi wa sallam) saw a man during a journey around whom people had gathered and were shading him. He asked, “What is the matter?” The people said, “He is fasting.” The Messenger of Allah (sallallahu alayhi wa sallam) said: “It is not righteousness that you fast while traveling.”
(Sahih Muslim, Book of Fasting, Hadith: 1115)

He (sallallahu alayhi wa sallam) also said: “Allah, the Exalted, says that His concessions should be accepted just as He dislikes that His commands be disobeyed.”
(Musnad Ahmad: 3/108)

If there is no hardship in fasting and someone fasts, there is no harm in it; but if there is hardship, then fasting is disliked (makruh).

The repetition of narrations is sometimes done to clarify certain subtleties in the chains of transmission, and according to the hadith scholars, this is a very beneficial and interesting matter, which has been indicated at several places. (For example, see Hadith: 2132)

Here, what is meant is not the continuous fasting of the entire year with consecutive fasts, because there is a strict prohibition of this in the ahadith, and such fasts are not valid according to the Shari‘ah. Upon examining the collective evidences, it becomes clear that here, by "continuous fasting" is meant fasting for a month or two consecutively, and nothing more. And Allah knows best. There is, insha’Allah, no hesitation regarding its permissibility.

Takhrij al-Hadith:
[وأخرجه البخاري 1943، من حديث مالك به ورواه مسلم 1121، من حديث هشام بن عروه به]

Fiqh:
➊ It is not obligatory to break the fast on every journey, and moreover, a supererogatory (nafl) fast can be observed while traveling.
➋ Also see: [الموطأ حديث : 50، 438]

Benefit 547:
From the aforementioned narration, it is understood that for a traveler, it is permissible not to fast during Ramadan while on a journey. However, during travel, it is more virtuous and better for him not to fast, because the statement of the Messenger of Allah (sallallahu alayhi wa sallam) is established: “Indeed, Allah, the Lord of Might and Majesty, loves that His concessions be accepted just as He dislikes that His commands be disobeyed.” [مسند احمد : 108/4]

Narrator of the Hadith:
Hazrat Hamzah bin Amr al-Aslami (radi Allahu anhu) was a Companion residing in Hijaz, whose kunyah was Abu Salih or Abu Muhammad. His son Muhammad and Umm al-Mu’minin Aisha Siddiqa (radi Allahu anha) narrate from him. He passed away in 61 AH, at which time he was 80 years old.