Muslim

Hadith Commentary:
This was a whisper (waswasah) that came into the heart of Ibn Mas'ud (radi Allahu anhu), but he immediately composed himself and refrained from entertaining this whisper.
It is derived from the hadith that during the night prayer, the Prophet (sallallahu alayhi wa sallam) used to recite (the Qur'an) at great length.

Hadith Commentary:
(1)
From this hadith, it is understood that the Messenger of Allah (sallallahu alayhi wa sallam) used to stand for long periods during the night prayer (tahajjud), because Abdullah ibn Mas'ud (radi Allahu anhu), despite being strong, intended to sit down during the standing (qiyam). This clearly means that the standing of the Messenger of Allah (sallallahu alayhi wa sallam) was quite lengthy.

In addition, the Messenger of Allah (sallallahu alayhi wa sallam) has declared the prayer with lengthy qunut (standing) to be the best prayer, as is found in Sahih Muslim.
(Sahih Muslim, Salat al-Musafirin, Hadith: 1768(756))

It is possible that in the hadith, by "lengthy qunut" is meant the lengthening of humility (khushu‘). The noble Companions (radi Allahu anhum) considered the abundance of bowing (ruku‘) and prostration (sujud) to be superior, as in another hadith it is mentioned that the abundance of prostration is a virtuous deed.
(Sahih Muslim, al-Salat, Hadith: 1093(488))

(2)
From this hadith, it is also understood that opposing the imam in the actions of prayer is a bad deed. Although Abdullah ibn Mas'ud (radi Allahu anhu) was legally permitted to sit, the respect and reverence for the elders takes precedence over this.
And Allah knows best.

Benefits and Issues:

➊ The congregational performance of the Tahajjud prayer is permissible.

➋ Lengthy recitation in the Tahajjud prayer is more virtuous.

➌ It is permissible to make students perform difficult tasks for the sake of their training, even if there is no hardship involved.

➍ When a teacher himself performs righteous deeds, it inspires enthusiasm and courage in the students to do the same.

➎ The noble Companions (radi Allahu anhum ajma'in) were so eager for righteousness that, by leaving a more virtuous act and opting for a merely permissible one, they considered it a bad deed.

➏ The intention of Hazrat Ibn Mas'ud (radi Allahu ta'ala anhu) was to perform prayer in the leadership of the Noble Prophet (sallallahu alayhi wa sallam). Now, the demand of following and loving is that one should accompany in this act of righteousness until the end. Therefore, he considered sitting down to be bad, as it is contrary to the demands of love.