Bukhari

Hadith Commentary:
➊ In this hadith, the great virtue of Abdullah ibn Umar (radi Allahu anhu) is described.
➋ Regarding him, the Messenger of Allah (sallallahu alayhi wa sallam) testified to his righteousness and piety.
➌ In this dream, Abdullah ibn Umar (radi Allahu anhu) was shown Hell in an exemplary manner, which had two edges; perhaps these edges are for admitting and removing the criminals.
➍ In one narration, it is mentioned that between these two edges there is an angel who holds an iron mace in his hand, and there are people hanging upside down there.
➎ The angels also said in the dream: "You are a very good man if you would be diligent in performing many voluntary prayers (nawafil)." Thus, Abdullah ibn Umar (radi Allahu anhu) adhered to night vigil (qiyam al-layl) until the end of his life.
(: Sahih al-Bukhari, Kitab al-Ta’bir, Hadith: 7028)

Hadith Commentary:
➊
Ibn Battal says that there are some dreams for which no interpretation is given, just as in the aforementioned dream, the Messenger of Allah (sallallahu alayhi wa sallam) did not provide any interpretation; rather, he simply narrated what he had seen in the dream. In the dream, the angel had said to him that "You are a good man; if only you would make a habit of performing the night prayer (tahajjud)." The Messenger of Allah (sallallahu alayhi wa sallam) repeated those very words.

➋
From this, it is understood that the source of interpretation is the statements of the Prophets (alayhimus-salam), as even Ibn Umar (radi Allahu anhu) himself desired this. However, interpretations of dreams from the Prophets (alayhimus-salam) are very rarely found. Nevertheless, this can be taken as a foundation to advance this discipline, just as a jurist (faqih) derives rulings and bases them on the statements of the Messenger of Allah (sallallahu alayhi wa sallam).

➌
Although this knowledge is not tawfiqi (i.e., not solely based on divine revelation), the foundation of this knowledge should be the interpretations given by the Prophets (alayhimus-salam). Instead of saying something from oneself, it is better and more blessed to refer back to the Book and the Sunnah.

(Fath al-Bari: 12/523)

Hadith Commentary:

From this hadith, it is understood that righteous deeds performed in youth are greatly beloved to Allah, the Most Holy, because Abdullah (radi Allahu anhu) was still a young man, and the angels were encouraging him towards righteous deeds, that is, voluntary prayers (nafl) and the night prayer (tahajjud).

Hadith Commentary:
➊
From this it is understood that if, while walking in a dream, one chooses the right side, its interpretation is that on the Day of Judgment he will be among the people of the right hand, that is, among the people of Paradise.
(Fath al-Bari: 12/524)

➋
This hadith also shows that righteous deeds performed in youth are very beloved to Allah Ta'ala, because Abdullah ibn Umar radi Allahu anhu was also young, and the angels were encouraging him towards righteous deeds, that is, to perform tahajjud and supererogatory prayers (nawafil). Thereafter, he made it a regular practice and would frequently perform tahajjud at night. Someone has beautifully said:
"In youth, to repent is the way of the Prophets.
In old age, even the cruel wolf becomes pious."

➌
This hadith also shows that an unmarried person can sleep in the mosque, and it is also permissible to appoint someone as a deputy to narrate a dream.
And Allah knows best.