Praise be to Allah, and peace and blessings be upon the Messenger of Allah and his family.
It is not permissible to combine all five prayers at one time, even if it is because of travelling. Indeed, it is not permissible to combine three prayers, so it is not correct to combine Maghrib, `Isha and Fajr, for example.
What is permitted is to combine Zuhr and `Asr , and Maghrib and `Isha’ , but Fajr cannot be combined with any other prayer.
The reason for this is that each one of the five prayers has its appointed time which is clearly defined, and which should be adhered to as it says in the Quran:
“… Verily, the prayer is enjoined on the believers at fixed hours.” [Al-Nisa 4:103]
This is also indicated by the hadith in which Jibril (peace be upon him) defined the times of each prayer and explained them to the Prophet (peace and blessings of Allah be upon him).
It was not reported that the Prophet (peace and blessings of Allah be upon him) combined all five prayers, only that he combined Zuhr and `Asr , and Maghrib and `Isha .
Acts of worship are based on reports, and combining prayers is an issue that has to do with acts of worship, so we should adhere to what it says in the texts and not try to take the matter any further. Ibn Daqiq al-‘Eid reported scholarly consensus on this issue, as did Ibn Hubayrah. Ibn Hajar al-Haythami said: “`Asr should not be combined with Maghrib, nor `Isha with Subh (Fajr), `Asr can only be combined with Zuhr, in accordance with what was reported.”
Al-Rafi’i (may Allah have mercy on him) said: “It is not permitted to combine Fajr prayer with any other prayer, or to combine `Asr and Maghrib, because no such thing was reported from the Messenger of Allah (peace and blessings of Allah be upon him).” (Al-Hafiz Ibn Hajar agreed with him in Talkhis al-Habir, 4/427)
Al-Nawawi said:
“It is not permitted to combine Fajr with any other prayer or to combine `Asr with Maghrib .”
And Allah knows best