A.T. Robertson Commentary Acts 16:25

"But about midnight Paul and Silas were praying and singing hymns unto God, and the prisoners were listening to them;" — Acts 16:25 (ASV)

About midnight (κατα δε μεσονυκτιον). Middle of the night, old adjective seen already in Mr 13:35; Luke 11:5 which see.

Were praying and singing (προσευχομενο υμνουν). Present middle participle and imperfect active indicative: Praying they were singing (simultaneously, blending together petition and praise). Hυμνεω is an old verb from υμνος (cf. Isaiah 12:4; Daniel 3:23). Paul and Silas probably used portions of the Psalms (cf. Luke 1:39f.,67f.; 2:28f.) with occasional original outbursts of praise.

Were listening to them (επηκροωντο αυτων). Imperfect middle of επακροαομα. Rare verb to listen with pleasure as to a recitation or music (Page). It was a new experience for the prisoners and wondrously attractive entertainment to them.