Bukhari

Hadith Commentary:
In this chapter, by "traveler" is meant the traveler on a journey of jihad.
After that, it applies to every traveler on a virtuous journey, due to which, out of necessity, many supererogatory acts, recitations, litanies, the night prayer (tahajjud), etc., are left out.
This is Allah’s grace, that for such a traveler, the reward for all those righteous supererogatory deeds continues to be granted—those deeds which he used to perform in a state of residence, but which are now left out due to travel.
The same ruling applies to a Muslim who is ill.
This is Allah’s grace, which is among the special characteristics of the Ummah of Muhammad (sallallahu alayhi wa sallam).
It is purely Allah’s grace that, whether in travel or residence, my humble work of compiling the commentary on Sahih al-Bukhari continues.
This is what I perform in place of supererogatory worship.
May Allah accept it and grant sincerity—Ameen.

Hadith Commentary:
➊
If someone is unable to fulfill an obligation due to illness or travel, then according to this hadith, it is hoped that he will not be deprived of the reward. For example: Standing during prayer is obligatory, but if, due to some necessity, one performs the prayer while sitting, the reward for standing will still be recorded for him. Similarly, during travel, many supererogatory prayers (nawafil), litanies (wazā’if), and regular practices are missed; it is the grace of Allah that the traveler continues to receive the reward for all those deeds which he used to perform while at home.

➋
In the title, the traveler refers to the one traveling for jihad, and then, by extension, anyone traveling for a righteous purpose is intended.

➌
It should be clear that this honor is for that traveler who, during his journey, spends his time in obedience to Allah and keeps himself away from sins.