Bukhari

Hadith Commentary:
But later they accepted Islam and were martyred immediately, thus entering Paradise.
That is, Allah was amazed at those people who will enter Paradise while they wore chains in the world; meaning, at first they were captured in battle and brought in shackles, then they happily became Muslim and attained Paradise.
From this hadith, Imam Bukhari rahimahullah established the permissibility of prisoners wearing chains.
That is, those who were captured in war and brought by the Muslims in chains, then they accepted Islam; or, those Muslims who were captured by the disbelievers and kept in chains, then died or were killed in that state, so they will be resurrected in that condition and will enter Paradise. This is as stated in "Al-Khair al-Jari." The summary of this statement is the same as what was mentioned above.

Hadith Commentary:
➊
The meaning of this hadith is that those people, having been shackled in chains in this world as prisoners of the Muslims, then willingly embraced Islam, and thereafter died with love for Islam and entered Paradise—that is, their being bound in chains became the cause for their entry into Paradise.

➋
From this hadith, Imam Bukhari rahimahullah has established the permissibility of placing chains on prisoners.

➌
Another meaning of this hadith is also mentioned: that it refers to those Muslims who are taken captive by the disbelievers and are made to wear chains, and then if they die in that state, they will enter Paradise—so did this captivity become the cause for their entry into Paradise? However, in our view, the first interpretation is more correct and is in accordance with the chapter heading established by Imam Bukhari rahimahullah.

And Allah knows best.

Benefits and Issues:
That is, some people are imprisoned while in a state of disbelief.
Then, after receiving guidance, they become Muslims.
So, insha Allah, they will enter Paradise.
It is understood from this that it is permissible to take prisoners captive.
And it has also been said that those Muslims who die or are martyred while in the captivity of the disbelievers will be resurrected in that very state.