A.T. Robertson Commentary Acts 10:46

"For they heard them speak with tongues, and magnify God. Then answered Peter," — Acts 10:46 (ASV)

They heard (ηκουον). Imperfect active, were hearing, kept on hearing.

Speak (λαλουντων). Present active participle, speaking, for they kept it up.

With tongues (γλωσσαις). Instrumental case as in 2:4,11 which see. The fuller statement there makes it clear that here it was new and strange tongues also as in 19:6; 1 Corinthians 14:4–19. This sudden manifestation of the Holy Spirit's power on uncircumcised Gentiles was probably necessary to convince Peter and the six brethren of the circumcision that God had opened the door wide to Gentiles. It was proof that a Gentile Pentecost had come and Peter used it effectively in his defence in Jerusalem (Acts 11:15).