John Gill Commentary Acts 12:6

"And when Herod was about to bring him forth, the same night Peter was sleeping between two soldiers, bound with two chains: and guards before the door kept the prison." — Acts 12:6 (ASV)

And when Herod would have brought him forth
The next morning; so he had determined not to dismiss him, but to expose him to the people, and to put him to such a death they should choose:

the same night, Peter was sleeping between two soldiers ;
fearless of death, being in a good cause, and having nothing to ruffle and disturb his mind; and though he was in a prison, and in such company, God gave him, his beloved, sleep:

bound with two chains ;
one on one hand, and one on the other, each of which were fastened to the soldiers; that on his right hand was fastened to the left hand of the soldier, that was on that side; and that on his left hand to the right hand of the soldier, on the other side him; such security was made, that he might not get away from them; to which is added,

and the keepers before the door kept the prison ;
or watched it, that nobody went in, or came out.