Bukhari

Hadith Commentary:
From this hadith, it is also derived that the one who combines prayers may eat food or engage in some work between the two prayers.
In this hadith, performing supererogatory (nafl) prayers along with combining (jam‘) is also mentioned.
Regarding Fajr, this was the opinion of Abdullah ibn Mas‘ud radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam performed the morning prayer in darkness on that day, and perhaps what he meant was that on that day it was performed in deep darkness, i.e., immediately at the break of true dawn (subh sadiq). Otherwise, many other Companions radi Allahu anhum have narrated that the habitual practice of the Prophet sallallahu alayhi wa sallam was to perform the Fajr prayer in darkness, and Umar radi Allahu anhu wrote to his governors instructing them to perform the morning prayer when the stars are dense, i.e., when it is still dark.
And it is also only the opinion of Ibn Mas‘ud that the Messenger of Allah sallallahu alayhi wa sallam did not combine prayers anywhere except at this place, whereas other Companions radi Allahu anhum have narrated that the Prophet sallallahu alayhi wa sallam combined prayers during travel.
(Wahidi)
He (Ibn Mas‘ud radi Allahu anhu) also performed supererogatory (nafl) prayers between Maghrib and ‘Isha, but it is established that the Messenger of Allah sallallahu alayhi wa sallam did not perform them, therefore the action of the Prophet sallallahu alayhi wa sallam will have preference.
However, if someone does perform them like Abdullah ibn Mas‘ud radi Allahu anhu, then most likely he will not be sinful, even though it will not be in accordance with the Sunnah of the Prophet.
Innamal a‘malu bin-niyyat (Actions are only by intentions).
The fundamental principle in religion is that the pleasure of Allah and His Messenger sallallahu alayhi wa sallam should always be given precedence.
Wherever a command is given for a particular action, that action should be done, and wherever there is a prohibition, one should refrain from it. This is the meaning of obedience, and in this lies goodness and well-being.
May Allah keep everyone steadfast upon the religion.

Hadith Commentary:
(1)
From this hadith, it is understood that when the Maghrib and Isha prayers are combined at Muzdalifah, it is prescribed to give a separate adhan and a separate iqamah for each prayer. It is narrated from Umar (radi Allahu anhu) that he performed both prayers at Muzdalifah and gave the adhan and iqamah for each prayer, and ate food in between. It is said that Umar (radi Allahu anhu) gave the adhan and iqamah for the second prayer because after Maghrib, people had dispersed after eating, so the adhan and iqamah were given to gather them again. Hafiz Ibn Hajar (rahimahullah) has considered this interpretation to be forced. In view of the apparent meaning of this hadith, Imam Malik (rahimahullah) has declared it prescribed to give a separate adhan and iqamah for Maghrib and Isha at Muzdalifah. Imam Bukhari (rahimahullah) has also adopted this position, but in Sahih Muslim, there is a narration from Jabir (radi Allahu anhu) that the Messenger of Allah (sallallahu alayhi wa sallam) combined Maghrib and Isha with one adhan and two iqamahs. (Fath al-Bari: 3/663) According to us, this is preferable; however, it is permissible to give a separate adhan and a separate takbir (iqamah) for each prayer.

(2)
From this hadith, it is evident that Abdullah ibn Mas'ud (radi Allahu anhu) performed two rak‘ahs after Maghrib, but it is established that the Messenger of Allah (sallallahu alayhi wa sallam) did not perform them, as we have mentioned earlier. On this basis, the practice of the Messenger of Allah (sallallahu alayhi wa sallam) is superior and preferred. However, if someone performs the sunnah after Maghrib, he cannot be called sinful. And Allah knows best.