Acts 16:25

And at midnight Paul and Silas prayed,
When others were asleep, and all things were still and quiet; (See Gill on Psalms 119:62), and they prayed doubtless for themselves, for their deliverance in God's time and way, and for support under their present afflictions; and for supplies of grace, to enable them to bear with patience and cheerfulness, until an issue was put to them; and for their enemies, and, particularly it may be for the jailer, who had used them so ill; and for the churches of Christ, for all the saints, and for the spread and success of the Gospel: and sang praises unto God;
or "sang an hymn to God", very likely one of David's psalms, or hymns: for the book of Psalms is a book, of hymns, and several of the psalms are particularly called hymns; this showed not only that they were cheerful, notwithstanding the stripes that were laid upon them, and though their feet were made fast in the stocks, and they were in the innermost prison, in a most loathsome and uncomfortable condition; and though they might be in expectation of greater punishment, and of death itself; but also that they were thankful and glorified God, who had counted them worthy to suffer for his name's sake: and the prisoners heard them;
for it seems there were other prisoners besides them, and who were in the outer prison: and from hence it appears, that their prayer was not merely mental; nor was their singing praises only a making melody in their hearts, but were both vocal; and it might be chiefly for the sake of the prisoners, that they both prayed and praised in this manner, that they might hear and be converted; or at least be convicted of the goodness of the cause, for which the apostles suffered.