Bukhari

Hadith Commentary:
The Prophet (sallallahu alayhi wa sallam) had the door of the noble Ka'bah closed after entering it so that others would not come inside, and in the form of a crowd, the original purpose of worship would be lost.
From this, it is understood that there was a chain on the door of the Ka'bah; this is precisely the subject of the chapter heading.
It is permissible to install doors in mosques for protection, and to use latches, locks, etc., on them.

Hadith Commentary:
1.
When the Messenger of Allah (sallallahu alayhi wa sallam) came to Makkah on the occasion of the Conquest of Makkah, he summoned the key-bearer of the Ka'bah, Hazrat Uthman bin Talhah (radi Allahu anhu), and requested the key from him. He opened the Ka'bah and entered inside, where he performed prayer. Due to the crowd, the door was closed from the inside.
Both aspects established by Imam Bukhari (rahimahullah) in the chapter heading are thus proven: that the Ka'bah had a door, and that it was closed when necessary.
It should be noted that in the era of ignorance (Jahiliyyah), the honorable and noble duties among the Quraysh were distributed among ten families. Among these, the service of providing water was assigned to Banu Hashim, while the key of the Ka'bah was with Banu Abd al-Dar, and its supervision was also entrusted to them.
Hazrat Uthman bin Talhah (radi Allahu anhu) was also from the descendants of Abd al-Dar. When the Messenger of Allah (sallallahu alayhi wa sallam) requested the key from Hazrat Uthman (radi Allahu anhu), he presented it. While delivering the sermon, the key was in the hand of the Prophet (sallallahu alayhi wa sallam).
Hazrat Ali (radi Allahu anhu) submitted that the key should be given to them so that the honor of custodianship could be combined with the service of providing Zamzam water. However, the Prophet (sallallahu alayhi wa sallam) called Hazrat Uthman bin Talhah (radi Allahu anhu) and said:
“O family of Abu Talhah! This key will remain with you forever and ever. No one will be able to take it from you except an oppressor or usurper.”
2 (: al-Mu’jam al-Kabir by al-Tabarani: 11/120.
In its chain is Abdullah bin Mu’ammal; Ibn Hajar said he is weak in hadith.)
In this narration, it is mentioned that Ibn Umar (radi Allahu anhu) forgot how many units (rak‘ahs) he had prayed. Whereas in Hadith number 397, it is mentioned that Hazrat Bilal (radi Allahu anhu) informed him that the Prophet (sallallahu alayhi wa sallam) had prayed two rak‘ahs. Ibn Hajar (rahimahullah) reconciled between these by stating that Hazrat Bilal (radi Allahu anhu) had indicated by gesture, but Abdullah bin Umar (radi Allahu anhu) forgot to clarify verbally.
(Fath al-Bari: 1/648)
And Allah knows best.