acts 16:26 And suddenly there was a great earthquake, so that the foundations of the prison were shaken: and immediately all the doors were opened, and every one's bands were loosed. - Free Bible Online

      26-28. And suddenly there was a great earthquake--in answer, doubtless, to the prayers and expectations of the sufferers that, for the truth's sake and the honor of their Lord, some interposition would take place.
      every one's bands--that is, the bands of all the prisoners.
      were loosed--not by the earthquake, of course, but by a miraculous energy accompanying it. By this and the joyous strains which they had heard from the sufferers, not to speak of the change wrought on the jailer, these prisoners could hardly fail to have their hearts in some measure opened to the truth; and this part of the narrative seems the result of information afterwards communicated by one or more of these men.

JFB.