Bukhari

Hadith Commentary:
Some incorrect concepts regarding the worship of Allah have existed in the religions of the world from the very beginning.
The Greatest Prophet (sallallahu alayhi wa sallam) was sent precisely to correct such misconceptions.
In the early days of Islam, some Companions also held such views.
Among them was Abu Darda (radi Allahu anhu), who believed that self-mortification to the extent of abandoning even permissible needs—such as forsaking rest at night and always fasting during the day—constituted worship, and that this alone was the means to Allah’s pleasure.
Salman (radi Allahu anhu) practically corrected this notion of his and demonstrated that fulfilling the rights of every rightful claimant is also included in the worship of Allah; fulfilling the rights of one’s wife, which includes having marital relations with her, is part of this.
Sleeping at night for rest, and eating and drinking during the day instead of continuously observing voluntary fasts—all these matters are included in worship.
When this incident between these two noble Companions reached the Messenger of Allah (sallallahu alayhi wa sallam), he supported Salman (radi Allahu anhu) and explained that the true concept of worship of Allah is that, along with fulfilling the rights of Allah, the rights of the servants—and even the rights of the self—should also be fulfilled.

Hadith Commentary:
(1)
With this heading, Imam Bukhari rahimahullah has begun to explain the rulings and issues related to voluntary (nafl) fasts. The first issue he presents regarding them is that after beginning a voluntary fast, it is necessary to complete it. If it is broken due to some need, is it obligatory to make it up (qada) or not? From the heading, it appears that Imam Bukhari rahimahullah inclines to the view that if it is broken for a valid reason, then making it up is not obligatory. However, if it is broken before its time without any reason, then its qada should be performed. Although the presented narration does not mention taking an oath, in Sunan al-Bayhaqi it is mentioned that Salman radi Allahu anhu said: "I ask you by oath to leave the fast." (Al-Sunan al-Kubra lil-Bayhaqi: 4/276)

(2)
From the presented narration, it is understood that a voluntary fast can be broken for a reasonable cause, and it is not necessary to complete it, nor is it obligatory to make it up. However, if a person wishes, he may keep another fast in its place later, as Abu Sa'id radi Allahu anhu narrates that he prepared food for the Messenger of Allah sallallahu alayhi wa sallam. He sallallahu alayhi wa sallam came along with his companions. When the food was presented, one man said: "I am fasting." The Messenger of Allah sallallahu alayhi wa sallam said: "Your brother has prepared food for you and has gone to great effort. Break your fast, and if you wish, keep a fast in its place later." (Al-Sunan al-Kubra lil-Bayhaqi: 4/279) These narrations indicate that a voluntary fast can be broken for a reason, and making it up is not obligatory, and the narrations that are presented as evidence for the obligation of qada are not valid as proof. (Fath al-Bari: 4/270)